U.S. patent application number 16/991096 was filed with the patent office on 2021-02-18 for synthesis of blue-emitting znse1-xtex alloy nanocrystals with low full width at half-maximum.
This patent application is currently assigned to NANOSYS, INC.. The applicant listed for this patent is NANOSYS, INC.. Invention is credited to Christian IPPEN, Ruiqing MA, Benjamin NEWMEYER.
Application Number | 20210047563 16/991096 |
Document ID | / |
Family ID | 1000005167495 |
Filed Date | 2021-02-18 |
United States Patent
Application |
20210047563 |
Kind Code |
A1 |
NEWMEYER; Benjamin ; et
al. |
February 18, 2021 |
SYNTHESIS OF BLUE-EMITTING ZnSe1-xTex ALLOY NANOCRYSTALS WITH LOW
FULL WIDTH AT HALF-MAXIMUM
Abstract
The invention pertains to the field of nanotechnology. The
invention provides highly luminescent nanostructures, particularly
highly luminescent nanostructures comprising a ZnSe.sub.1-x
Te.sub.x core and ZnS and/or ZnSe shell layers. The nanostructures
comprising a ZnSe.sub.1-xTe.sub.x core and ZnS and/or ZnSe shell
layers display a low full width at half-maximum and a high quantum
yield. The invention also provides methods of producing the
nanostructures.
Inventors: |
NEWMEYER; Benjamin; (San
Jose, CA) ; IPPEN; Christian; (Cupertino, CA)
; MA; Ruiqing; (Morristown, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NANOSYS, INC. |
Milpitas |
CA |
US |
|
|
Assignee: |
NANOSYS, INC.
Milpitas
CA
|
Family ID: |
1000005167495 |
Appl. No.: |
16/991096 |
Filed: |
August 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62885469 |
Aug 12, 2019 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/883 20130101;
H01L 33/06 20130101; H01L 2933/0041 20130101; B82Y 20/00 20130101;
H01L 33/005 20130101; H01L 33/502 20130101 |
International
Class: |
C09K 11/88 20060101
C09K011/88; H01L 33/06 20060101 H01L033/06; H01L 33/50 20060101
H01L033/50; H01L 33/00 20060101 H01L033/00 |
Claims
1. A nanostructure comprising a core surrounded by at least one
shell, wherein the core comprises ZnSe.sub.1-xTe.sub.x, wherein
0<x<1, wherein the at least one shell is selected from the
group consisting of ZnS, ZnSe, ZnTe, and alloys thereof, and
wherein the full width at half maximum (FWHM) of the nanostructure
is about 20 nm to about 30 nm.
2. The nanostructure of claim 1, wherein the FWHM is about 25 nm to
about 30 nm.
3. The nanostructure of claim 1, wherein the emission wavelength of
the nanostructure is between about 440 nm and about 460 nm.
4. The nanostructure of claim 1, wherein the emission wavelength of
the nanostructure is between 450 nm and 460 nm.
5. The nanostructure of claim 1, wherein the core is surrounded by
two shells.
6. (canceled)
7. The nanostructure of claim 1, wherein at least one shell
comprises ZnSe.
8. The nanostructure of claim 1, wherein at least one shell
comprises ZnS.
9. The nanostructure of claim 1, wherein at least one shell
comprises between about 4 and about 6 monolayers of ZnSe.
10. The nanostructure of claim 1, wherein at least one shell
comprises about 6 monolayers of ZnSe.
11. The nanostructure of claim 1, wherein at least one shell
comprises between about 4 and about 6 monolayers of ZnS.
12. The nanostructure of claim 1, wherein the at least one shell
comprises about 4 monolayers of ZnS.
13. The nanostructure of claim 1, wherein the photoluminescence
quantum yield of the nanostructure is between about 75% and about
90%.
14. The nanostructure of claim 1, wherein the photoluminescence
quantum yield of the nanostructure is between 80% and 90%.
15. (canceled)
16. The nanostructure of claim 1, wherein the nanostructure
comprises two shells, wherein the first shell comprises ZnSe and
the second shell comprises ZnS.
17. The nanostructure of claim 1, wherein the nanostructure is a
quantum dot.
18. The nanostructure of claim 1, wherein the nanostructure is free
of cadmium.
19. A device comprising the nanostructure of claim 1.
20. A method of producing a ZnSe.sub.1-xTe.sub.x nanocrystal
comprising: (a) admixing a tellurium source, at least one ligand,
and a reducing agent to produce a reaction mixture; (b) contacting
the reaction mixture obtained in (a) with a solution comprising at
least one ligand, zinc fluoride, and a selenium source; and (c)
contacting the reaction mixture obtained in (b) with a zinc source;
to provide a ZnSe.sub.1-xTe.sub.x nanocrystal.
21.-46. (canceled)
47. A method of producing a core/shell nanostructure comprising:
(e) admixing the ZnSe.sub.1-xTe.sub.x nanocrystal prepared by the
method of claim 20 with a solution comprising a zinc source; (f)
contacting the reaction mixture of (e) with a selenium source or a
sulfur source.
48.-70. (canceled)
71. A nanostructure molded article comprising: (a) a first
conductive layer; (b) a second conductive layer; and (c) a
nanostructure layer between the first conductive layer and the
second conductive layer, wherein the nanostructure layer comprises
a population of nanostructures comprising a core surrounded by at
least one shell, wherein the core comprises ZnSe.sub.1-xTe.sub.x,
wherein 0<x<1, wherein the at least one shell is selected
from the group consisting of ZnS, ZnSe, ZnTe, and alloys thereof,
and wherein the full width at half maximum (FWHM) of the
nanostructure is about 20 nm to about 30 nm.
72.-83. (canceled)
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The invention pertains to the field of nanotechnology. The
invention provides highly luminescent nanostructures, particularly
highly luminescent nanostructures comprising a ZnSe.sub.1-xTe.sub.x
core and ZnS and/or ZnSe shell layers. The nanostructures
comprising a ZnSe.sub.1-xTe.sub.x core and ZnS and/or ZnSe shell
layers display a low full width at half-maximum and a high quantum
yield. The invention also provides methods of producing the
nanostructures.
Background Art
[0002] Semiconductor nanostructures can be incorporated into a
variety of electronic and optical devices. The electrical and
optical properties of such nanostructures vary, e.g., depending on
their composition, shape, and size. For example, size-tunable
properties of semiconductor nanoparticles are of great interest for
applications such as light emitting diodes (LEDs), lasers, and
biomedical labeling. Highly luminescent nanostructures are
particularly desirable for such applications.
[0003] To exploit the full potential of nanostructures in
applications such as LEDs and displays, the nanostructures need to
simultaneously meet five criteria: narrow and symmetric emission
spectra, high photoluminescence (PL) quantum yields (QYs), high
optical stability, eco-friendly materials, and low-cost methods for
mass production. Most previous studies on highly emissive and
color-tunable quantum dots have concentrated on materials
containing cadmium, mercury, or lead. Wang, A., et al., Nanoscale
7:2951-2959 (2015). But, there are increasing concerns that toxic
materials such as cadmium, mercury, or lead would pose serious
threats to human health and the environment and the European
Union's Restriction of Hazardous Substances rules ban any consumer
electronics containing more than trace amounts of these materials.
Therefore, there is a need to produce materials that are free of
cadmium, mercury, and lead for the production of LEDs and
displays.
[0004] Electroluminescent quantum dot light-emitting devices with
BT.2020 color gamut require a blue-emitting quantum dot material
with a peak wavelength in the range of 450 nm to 460 nm with less
than a 30 nm full width at half-maximum (FWHM) and high quantum
yield. For regulatory compliance, the material needs to be free of
cadmium and lead.
[0005] It is difficult to achieve these parameters with
cadmium-free materials. As described in Ning, J., et al., Chem.
Commun. 53:2626-2629 (2017), indium phosphide quantum dots grown
from magic size clusters as the smallest imaginable core show a
minimum photoluminescence peak of 460 nm (with >50 nm FWHM and
low quantum yield) and red shift upon shell coating. As described
in U.S. Patent Appl. No. 2017/0066965, ZnSe quantum dots can be
made with very sharp emission peaks and high quantum yields at a
peak wavelength of up to 435 nm, but further particle growth
towards the target wavelength resulted in significant quantum yield
loss due to poor electron-hole overlap in giant cores.
[0006] A need exists to prepare nanostructure compositions that
have a peak emission wavelength in the range of 440 nm to 460 nm
and a FWHM of less than 30 nm.
BRIEF SUMMARY OF THE INVENTION
[0007] The present disclosure provides a nanostructure comprising a
core surrounded by at least one shell, wherein the core comprises
ZnSe.sub.1-xTe.sub.x, wherein 0<x<1, wherein the at least one
shell is selected from the group consisting of ZnS, ZnSe, ZnTe, and
alloys thereof, and wherein the full width at half maximum (FWHM)
of the nanostructure is about 20 nm to about 30 nm.
[0008] In some embodiments, the FWHM is about 25 nm to about 30
nm.
[0009] In some embodiments, the emission wavelength of the
nanostructure is between about 440 nm and about 460 nm. In some
embodiments, the emission wavelength of the nanostructure is
450-460 nm.
[0010] In some embodiments, the core of the nanostructure is
surrounded by two shells.
[0011] In some embodiments, at least one shell of the nanostructure
comprises ZnS or ZnSe.
[0012] In some embodiments, at least one shell of the nanostructure
comprises ZnSe.
[0013] In some embodiments, at least one shell of the nanostructure
comprises ZnS.
[0014] In some embodiments, at least one shell of the nanostructure
comprises between about 4 and about 6 monolayers of ZnSe.
[0015] In some embodiments, at least one shell of the nanostructure
comprises about 6 monolayers of ZnSe.
[0016] In some embodiments, at least one shell of the nanostructure
comprises between about 4 and about 6 monolayers of ZnS.
[0017] In some embodiments, at least one shell of the nanostructure
comprises about 4 monolayers of ZnS.
[0018] In some embodiments, the photoluminescence quantum yield of
the nanostructure is between about 75% and about 90%.
[0019] In some embodiments, the photoluminescence quantum yield of
the nanostructure is between 80% and 90%.
[0020] In some embodiments, the FWHM of the nanostructure is
between about 15 nm and about 19 nm.
[0021] In some embodiments, the nanostructure comprises two shells,
wherein the first shell comprises ZnSe and the second shell
comprises ZnS.
[0022] In some embodiments, the nanostructure is a quantum dot.
[0023] In some embodiments, the nanostructure is free of
cadmium.
[0024] In some embodiments, a device comprising the nanostructure
of the present disclosure is provided.
[0025] The present disclosure also provides a method of producing a
ZnSe.sub.1-xTe.sub.x nanocrystal comprising:
[0026] (a) admixing a tellurium source, at least one ligand, and a
reducing agent to produce a reaction mixture;
[0027] (b) contacting the reaction mixture obtained in (a) with a
solution comprising at least one ligand, zinc fluoride, and a
selenium source; and
[0028] (c) contacting the reaction mixture obtained in (b) with a
zinc source; to provide a ZnSe.sub.1-xTe.sub.x nanocrystal.
[0029] In some embodiments, the selenium source is selected from
the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof. In some embodiments, the selenium source is
trioctylphosphine selenide.
[0030] In some embodiments, the at least one ligand in (b) is
selected from the group consisting of trioctylphosphine oxide,
trioctylphosphine, diphenylphosphine, triphenylphosphine oxide, and
tributylphosphine oxide. In some embodiments, the at least one
ligand in (b) is diphenylphosphine.
[0031] In some embodiments, the tellurium source is selected from
the group consisting of trioctylphosphine telluride,
tri(n-butyl)phosphine telluride, trimethylphosphine telluride,
triphenylphosphine telluride, tricyclohexylphosphine telluride,
elemental tellurium, hydrogen telluride, bis(trimethylsilyl)
telluride, and mixtures thereof. In some embodiments, the tellurium
source is trioctylphosphine telluride.
[0032] In some embodiments, the reducing agent is selected from the
group consisting of diborane, sodium hydride, sodium borohydride,
lithium borohydride, sodium cyanoborohydride, calcium hydride,
lithium hydride, lithium aluminum hydride, diisobutylaluminum
hydride, sodium triethylborohydride, and lithium
triethylborohydride. In some embodiments, the reducing agent is
lithium triethylborohydride.
[0033] In some embodiments, the zinc source in (c) is selected from
the group consisting of diethylzinc, dimethylzinc, diphenylzinc,
zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc
chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc
nitrate, zinc oxide, zinc peroxide, zinc perchlorate, and zinc
sulfate. In some embodiments, the zinc source in (c) is
diethylzinc.
[0034] In some embodiments, the method further comprises: (d)
contacting the reaction mixture in (c) with a zinc carboxylate and
a selenium source.
[0035] In some embodiments, the zinc carboxylate in (d) is selected
from the group consisting of zinc oleate, zinc hexanoate, zinc
octanoate, zinc laurate, zinc myristate, zinc palmitate, zinc
stearate, zinc dithiocarbamate, and mixtures thereof. In some
embodiments, the zinc carboxylate in (d) is zinc oleate.
[0036] In some embodiments, the selenium source in (d) is selected
from the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof. In some embodiments, the selenium source in (d) is
trioctylphosphine selenide.
[0037] In some embodiments, the admixing in (a) is at about room
temperature.
[0038] In some embodiments, the contacting in (b) is at a
temperature between about 250.degree. C. and about 350.degree. C.
In some embodiments, the contacting in (b) is at a temperature of
about 280.degree. C.
[0039] In some embodiments, the contacting in (c) is at a
temperature between about 250.degree. C. and about 350.degree. C.
In some embodiments, the contacting in (c) is at a temperature of
about 280.degree. C.
[0040] In some embodiments, the contacting in (c) further comprises
at least one ligand. In some embodiments, the at least one ligand
is trioctylphosphine or diphenylphosphine.
[0041] In some embodiments, the contacting in (d) is at a
temperature between about 250.degree. C. and about 350.degree. C.
In some embodiments, the contacting in (d) is at a temperature of
about 310.degree. C.
[0042] In some embodiments, the contacting in (d) further comprises
at least one ligand. In some embodiments, the at least one ligand
is trioctylphosphine or diphenylphosphine.
[0043] The disclosure further provides method of producing a
core/shell nanostructure comprising:
[0044] (e) admixing the ZnSe.sub.1-xTe.sub.x nanocrystal prepared
by any one of the methods above with a solution comprising a zinc
source; and
[0045] (f) contacting the reaction mixture of (e) with a selenium
source or a sulfur source.
[0046] In some embodiments, the method further comprises:
[0047] (g) contacting the reaction mixture of (f) with a selenium
source or a sulfur source; wherein the source used in (g) is
different than the source used in (f).
[0048] In some embodiments, the admixing in (e) is at a temperature
between about 20.degree. C. and about 310.degree. C. In some
embodiments, the admixing in (e) is at a temperature between about
20.degree. C. and about 100.degree. C.
[0049] In some embodiments, the zinc source of (e) is selected from
the group consisting of diethylzinc, dimethylzinc, diphenylzinc,
zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc
chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc
nitrate, zinc oleate, zinc oxide, zinc peroxide, zinc perchlorate,
zinc sulfate, zinc hexanoate, zinc octanoate, zinc laurate, zinc
myristate, zinc palmitate, zinc stearate, zinc dithiocarbamate,
zinc oleate, zinc hexanoate, zinc octanoate, zinc laurate, zinc
myristate, zinc palmitate, zinc stearate, zinc dithiocarbamate, and
mixtures thereof.
[0050] In some embodiments, the contacting in (f) is at a
temperature between about 200.degree. C. and about 350.degree. C.
In some embodiments, the contacting in (f) is at a temperature of
about 310.degree. C.
[0051] In some embodiments, in (f) the reaction mixture is
contacted with a selenium source. In some embodiments, the selenium
source is selected from the group consisting of trioctylphosphine
selenide, tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine
selenide, tri(tert-butyl)phosphine selenide, trimethylphosphine
selenide, triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0052] In some embodiments, in (f) the reaction mixture is
contacted with a sulfur source. In some embodiments, the sulfur
source is selected from the group consisting of elemental sulfur,
octanethiol, dodecanethiol, octadecanethiol, tributylphosphine
sulfide, cyclohexyl isothiocyanate, .alpha.-toluenethiol, ethylene
trithiocarbonate, allyl mercaptan, bis(trimethylsilyl) sulfide,
trioctylphosphine sulfide, and mixtures thereof.
[0053] In some embodiments, the contacting in (f) is at a
temperature between about 200.degree. C. and about 350.degree. C.
In some embodiments, the contacting in (f) is at a temperature of
about 310.degree. C.
[0054] In some embodiments, in (g) the reaction mixture is
contacted with a selenium source. In some embodiments, the selenium
source is selected from the group consisting of trioctylphosphine
selenide, tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine
selenide, tri(tert-butyl)phosphine selenide, trimethylphosphine
selenide, triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0055] In some embodiments, in (g) the reaction mixture is
contacted with a sulfur source. In some embodiments, the sulfur
source is selected from the group consisting of elemental sulfur,
octanethiol, dodecanethiol, octadecanethiol, tributylphosphine
sulfide, cyclohexyl isothiocyanate, .alpha.-toluenethiol, ethylene
trithiocarbonate, allyl mercaptan, bis(trimethylsilyl) sulfide,
trioctylphosphine sulfide, and mixtures thereof.
[0056] In some embodiments, the admixing in (e) further comprises
at least one ligand. In some embodiments, the at least one ligand
is selected from the group consisting of trioctylphosphine oxide,
trioctylphosphine, diphenylphosphine, triphenylphosphine oxide, and
tributylphosphine oxide. In some embodiments, the at least one
ligand is trioctylphosphine or trioctylphosphine oxide.
[0057] In some embodiments, the nanostructure displays a
photoluminescence quantum yield of between about 75% and about 90%.
In some embodiments, the nanostructure displays a photoluminescence
quantum yield of between about 80% and about 90%.
[0058] In some embodiments, the nanostructure has a full width at
half-maximum of about 20 nm to about 30 nm. In some embodiments,
the nanostructure has a full width at half-maximum of between about
25 nm and about 30 nm.
[0059] The present disclosure also provides a method of producing a
ZnSe.sub.1-xTe.sub.x nanocrystal comprising:
[0060] (a) admixing a selenium source and at least one ligand to
produce a reaction mixture;
[0061] (b) contacting the reaction mixture obtained in (a) with a
solution comprising a tellurium source, a reducing agent, and a
zinc carboxylate; and
[0062] (c) contacting the reaction mixture obtained in (b) with a
zinc source; to provide a ZnSe.sub.1-xTe.sub.x nanocrystal.
[0063] In some embodiments, the selenium source admixed in (a) is
selected from the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0064] In some embodiments, the selenium source admixed in (a) is
trioctylphosphine selenide.
[0065] In some embodiments, the at least one ligand admixed in (a)
is selected from the group consisting of trioctylphosphine oxide,
trioctylphosphine, diphenylphosphine, triphenylphosphine oxide, and
tributylphosphine oxide.
[0066] In some embodiments, the at least one ligand admixed in (a)
is trioctylphosphine.
[0067] In some embodiments, the tellurium source in (b) is selected
from the group consisting of trioctylphosphine telluride,
tri(n-butyl)phosphine telluride, trimethylphosphine telluride,
triphenylphosphine telluride, tricyclohexylphosphine telluride,
elemental tellurium, hydrogen telluride, bis(trimethylsilyl)
telluride, and mixtures thereof.
[0068] In some embodiments, the tellurium source in (b) is
trioctylphosphine telluride.
[0069] In some embodiments, the reducing agent in (b) is selected
from the group consisting of diborane, sodium hydride, sodium
borohydride, lithium borohydride, sodium cyanoborohydride, calcium
hydride, lithium hydride, lithium aluminum hydride,
diisobutylaluminum hydride, sodium triethylborohydride, and lithium
triethylborohydride.
[0070] In some embodiments, the reducing agent in (b) is lithium
triethylborohydride.
[0071] In some embodiments, the zinc carboxylate in (b) is selected
from the group consisting of zinc oleate, zinc hexanoate, zinc
octanoate, zinc laurate, zinc myristate, zinc palmitate, zinc
stearate, zinc dithiocarbamate, and mixtures thereof.
[0072] In some embodiments, the zinc carboxylate in (b) is zinc
oleate.
[0073] In some embodiments, the zinc source in (c) is selected from
the group consisting of diethylzinc, dimethylzinc, diphenylzinc,
zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc
chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc
nitrate, zinc oxide, zinc peroxide, zinc perchlorate, and zinc
sulfate.
[0074] In some embodiments, the zinc source in (c) is
diethylzinc.
[0075] In some embodiments, the method of producing a
ZnSe.sub.1-xTe.sub.x nanocrystal comprising, further comprises:
[0076] (d) contacting the reaction mixture in (c) with a zinc
source and a selenium source.
[0077] In some embodiments, the zinc source in (d) is selected from
the group consisting of diethylzinc, dimethylzinc, diphenylzinc,
zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc
chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc
nitrate, zinc oxide, zinc peroxide, zinc perchlorate, and zinc
sulfate.
[0078] In some embodiments, the zinc source in (d) is
diethylzinc.
[0079] In some embodiments, the selenium source in (d) is selected
from the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0080] In some embodiments, the selenium source in (d) is
trioctylphosphine selenide.
[0081] In some embodiments, the admixing in (a) is at a temperature
between about 250.degree. C. and about 350.degree. C.
[0082] In some embodiments, the admixing in (a) is at a temperature
of about 300.degree. C.
[0083] In some embodiments, the contacting in (b) is at a
temperature between about 250.degree. C. and about 350.degree.
C.
[0084] In some embodiments, the contacting in (b) is at a
temperature of about 300.degree. C.
[0085] In some embodiments, the contacting in (b) further comprises
at least one ligand.
[0086] In some embodiments, the contacting in (c) is at a
temperature between about 250.degree. C. and about 350.degree.
C.
[0087] In some embodiments, the contacting in (c) is at a
temperature of about 300.degree. C.
[0088] In some embodiments, the contacting in (c) further comprises
at least one ligand. In some embodiments, the at least one ligand
is trioctylphosphine or diphenylphosphine.
[0089] In some embodiments, the contacting in (d) is at a
temperature between about 250.degree. C. and about 350.degree.
C.
[0090] In some embodiments, the contacting in (d) is at a
temperature of about 300.degree. C.
[0091] In some embodiments, the contacting in (d) further comprises
at least one ligand.
[0092] In some embodiments, the at least one ligand is
trioctylphosphine or diphenylphosphine.
[0093] In some embodiments, the selenium source in (a) is
trioctylphosphine selenide, the tellurium source in (b) is
trioctylphosphine telluride, the reducing agent in (b) is lithium
triethylborohydride, the zinc carboxylate in (b) is zinc oleate,
and the zinc source in (c) in diethylzinc.
[0094] In some embodiments, the selenium source in (a) and (c) is
trioctylphosphine selenide, the tellurium source in (b) is
trioctylphosphine telluride, the reducing agent in (b) is lithium
triethylborohydride, the zinc carboxylate in (b) is zinc oleate,
and the zinc source in (c) and (d) is diethylzinc,
[0095] The present disclosure provides a method of producing a
core/shell nanostructure comprising:
[0096] (e) admixing the ZnSe.sub.1-xTe.sub.x nanocrystal prepared
by a method disclosed herein with a solution comprising a zinc
source;
[0097] (f) contacting the reaction mixture of (e) with a selenium
source or a sulfur source.
[0098] In some embodiments, the method of producing a core/shell
nanostructure further comprises:
[0099] (g) contacting the reaction mixture of (f) with a selenium
source or a sulfur source; wherein the source used in (g) is
different than the source used in (f).
[0100] In some embodiments, the admixing in (e) is at a temperature
between about 20.degree. C. and about 310.degree. C.
[0101] In some embodiments, the admixing in (e) is at a temperature
between about 20.degree. C. and about 100.degree. C.
[0102] In some embodiments, the zinc source of (e) is selected from
the group consisting of diethylzinc, dimethylzinc, diphenylzinc,
zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc
chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc
nitrate, zinc oleate, zinc oxide, zinc peroxide, zinc perchlorate,
zinc sulfate, zinc hexanoate, zinc octanoate, zinc laurate, zinc
myristate, zinc palmitate, zinc stearate, zinc dithiocarbamate,
zinc oleate, zinc hexanoate, zinc octanoate, zinc laurate, zinc
myristate, zinc palmitate, zinc stearate, zinc dithiocarbamate, and
mixtures thereof.
[0103] In some embodiments, the contacting in (f) is at a
temperature between about 200.degree. C. and about 350.degree.
C.
[0104] In some embodiments, the contacting in (f) is at a
temperature of about 310.degree. C.
[0105] In some embodiments, the reaction mixture in (f) is
contacted with a selenium source.
[0106] In some embodiments, the selenium source is selected from
the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0107] In some embodiments, the reaction mixture in (f) is
contacted with a sulfur source.
[0108] In some embodiments, the sulfur source is selected from the
group consisting of elemental sulfur, octanethiol, dodecanethiol,
octadecanethiol, tributylphosphine sulfide, cyclohexyl
isothiocyanate, .alpha.-toluenethiol, ethylene trithiocarbonate,
allyl mercaptan, bis(trimethylsilyl) sulfide, trioctylphosphine
sulfide, and mixtures thereof.
[0109] In some embodiments, the contacting in (f) is at a
temperature between about 200.degree. C. and about 350.degree.
C.
[0110] In some embodiments, the contacting in (f) is at a
temperature of about 310.degree. C.
[0111] In some embodiments, the reaction mixture in (g) is
contacted with a selenium source.
[0112] In some embodiments, the selenium source is selected from
the group consisting of trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, cyclohexylphosphine selenide,
octaselenol, dodecaselenol, selenophenol, elemental selenium,
hydrogen selenide, bis(trimethylsilyl) selenide, and mixtures
thereof.
[0113] In some embodiments, the reaction mixture in (g) is
contacted with a sulfur source.
[0114] In some embodiments, the sulfur source is selected from the
group consisting of elemental sulfur, octanethiol, dodecanethiol,
octadecanethiol, tributylphosphine sulfide, cyclohexyl
isothiocyanate, .alpha.-toluenethiol, ethylene trithiocarbonate,
allyl mercaptan, bis(trimethylsilyl) sulfide, trioctylphosphine
sulfide, and mixtures thereof.
[0115] In some embodiments, the admixing in (e) further comprises
at least one ligand.
[0116] In some embodiments, the at least one ligand is selected
from the group consisting of trioctylphosphine oxide,
trioctylphosphine, diphenylphosphine, triphenylphosphine oxide, and
tributylphosphine oxide.
[0117] In some embodiments, the at least one ligand is
trioctylphosphine or trioctylphosphine oxide.
[0118] In some embodiments, the nanostructure provided by the
method displays a photoluminescence quantum yield of between about
75% and about 90%.
[0119] In some embodiments, the nanostructure provided by the
method displays a photoluminescence quantum yield of between about
80% and about 90%.
[0120] In some embodiments, the nanostructure provided by the
method has a full width at half-maximum of about 20 nm to about 30
nm.
[0121] In some embodiments, the nanostructure provided by the
method has a full width at half-maximum of between about 15 nm and
about 19 nm.
[0122] The present disclosure also provides a nanostructure molded
article comprising:
[0123] (a) a first conductive layer;
[0124] (b) a second conductive layer; and
[0125] (c) a nanostructure layer between the first conductive layer
and the second conductive layer, wherein the nanostructure layer
comprises a population of nanostructures comprising a core
surrounded by at least one shell, wherein the core comprises
ZnSe.sub.1-xTe.sub.x, wherein 0<x<1, wherein the at least one
shell is selected from the group consisting of ZnS, ZnSe, ZnTe, and
alloys thereof, and wherein the full width at half maximum (FWHM)
of the nanostructure is about 20 nm to about 30 nm.
[0126] In some embodiments, the nanostructure in the nanostructure
molded article comprises two shells.
[0127] In some embodiments, at least one shell of the nanostructure
in the nanostructure molded article is selected from the group
consisting of wherein at least one shell comprises ZnS or ZnSe.
[0128] In some embodiments, at least one shell of the nanostructure
in the nanostructure molded article comprises ZnSe.
[0129] In some embodiments, at least one shell of the nanostructure
in the nanostructure molded article comprises ZnS.
[0130] In some embodiments, at least two shells of the
nanostructure in the nanostructure molded article comprise
zinc.
[0131] In some embodiments, at least one shell of the nanostructure
in the nanostructure molded article comprises ZnSe and at least one
shell comprises ZnS.
[0132] In some embodiments, the nanostructure in the nanostructure
molded article exhibits a photoluminescence quantum yield of
between about 75% and about 90%.
[0133] In some embodiments, the nanostructure in the nanostructure
molded article exhibits a photoluminescence quantum yield of
between about 80% and about 90%.
[0134] In some embodiments, the nanostructure in the nanostructure
molded article exhibits a full width at half-maximum of about 20 nm
to about 30 nm.
[0135] In some embodiments, the nanostructure molded article
exhibits a full width at half-maximum of between about 15 nm and
about 19 nm.
[0136] In some embodiments, the nanostructures in the nanostructure
molded article comprise at least one shell comprising ZnSe, and at
least one shell comprising ZnS.
[0137] In some embodiments, the nanostructures in the nanostructure
molded article are quantum dots.
BRIEF DESCRIPTION OF THE DRAWINGS
[0138] FIG. 1 is a flowchart comparing the synthesis of a
ZnSe.sub.1-xTe.sub.x core using the co-injection method and
synthesis of a ZnSe.sub.1-xTe.sub.x core using the offset injection
method.
[0139] FIG. 2 shows photoluminescence spectra in solution for a
ZnSe core, for a ZnSe.sub.1-xTe.sub.x core prepared using the
co-injection method, and for a ZnSe.sub.1-xTe.sub.x core prepared
using the offset injection method.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0140] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which the invention pertains. The
following definitions supplement those in the art and are directed
to the current application and are not to be imputed to any related
or unrelated case, e.g., to any commonly owned patent or
application. Although any methods and materials similar or
equivalent to those described herein can be used in the practice
for testing of the present invention, the preferred materials and
methods are described herein. Accordingly, the terminology used
herein is for the purpose of describing particular embodiments
only, and is not intended to be limiting.
[0141] As used in this specification and the appended claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly dictates otherwise. Thus, for example,
reference to "a nanostructure" includes a plurality of such
nanostructures, and the like.
[0142] The term "about" as used herein indicates the value of a
given quantity varies by +/-10% of the value so described. For
example, "about 100 nm" encompasses a range of sizes from 90 nm to
110 nm, inclusive.
[0143] A "nanostructure" is a structure having at least one region
or characteristic dimension with a dimension of less than about 500
nm. In some embodiments, the nanostructure has a dimension of less
than about 200 nm, less than about 100 nm, less than about 50 nm,
less than about 20 nm, or less than about 10 nm. Typically, the
region or characteristic dimension will be along the smallest axis
of the structure. Examples of such structures include nanowires,
nanorods, nanotubes, branched nanostructures, nanotetrapods,
tripods, bipods, nanocrystals, nanodots, quantum dots,
nanoparticles, and the like. Nanostructures can be, e.g.,
substantially crystalline, substantially monocrystalline,
polycrystalline, amorphous, or a combination thereof. In some
embodiments, each of the three dimensions of the nanostructure has
a dimension of less than about 500 nm, less than about 200 nm, less
than about 100 nm, less than about 50 nm, less than about 20 nm, or
less than about 10 nm.
[0144] The term "heterostructure" when used with reference to
nanostructures refers to nanostructures characterized by at least
two different and/or distinguishable material types. Typically, one
region of the nanostructure comprises a first material type, while
a second region of the nanostructure comprises a second material
type. In certain embodiments, the nanostructure comprises a core of
a first material and at least one shell of a second (or third etc.)
material, where the different material types are distributed
radially about the long axis of a nanowire, a long axis of an arm
of a branched nanowire, or the center of a nanocrystal, for
example. A shell can but need not completely cover the adjacent
materials to be considered a shell or for the nanostructure to be
considered a heterostructure; for example, a nanocrystal
characterized by a core of one material covered with small islands
of a second material is a heterostructure. In other embodiments,
the different material types are distributed at different locations
within the nanostructure; e.g., along the major (long) axis of a
nanowire or along a long axis of arm of a branched nanowire.
Different regions within a heterostructure can comprise entirely
different materials, or the different regions can comprise a base
material (e.g., silicon) having different dopants or different
concentrations of the same dopant.
[0145] As used herein, the "diameter" of a nanostructure refers to
the diameter of a cross-section normal to a first axis of the
nanostructure, where the first axis has the greatest difference in
length with respect to the second and third axes (the second and
third axes are the two axes whose lengths most nearly equal each
other). The first axis is not necessarily the longest axis of the
nanostructure; e.g., for a disk-shaped nanostructure, the
cross-section would be a substantially circular cross-section
normal to the short longitudinal axis of the disk. Where the
cross-section is not circular, the diameter is the average of the
major and minor axes of that cross-section. For an elongated or
high aspect ratio nanostructure, such as a nanowire, the diameter
is measured across a cross-section perpendicular to the longest
axis of the nanowire. For a spherical nanostructure, the diameter
is measured from one side to the other through the center of the
sphere.
[0146] The terms "crystalline" or "substantially crystalline," when
used with respect to nanostructures, refer to the fact that the
nanostructures typically exhibit long-range ordering across one or
more dimensions of the structure. It will be understood by one of
skill in the art that the term "long range ordering" will depend on
the absolute size of the specific nanostructures, as ordering for a
single crystal cannot extend beyond the boundaries of the crystal.
In this case, "long-range ordering" will mean substantial order
across at least the majority of the dimension of the nanostructure.
In some instances, a nanostructure can bear an oxide or other
coating, or can be comprised of a core and at least one shell. In
such instances it will be appreciated that the oxide, shell(s), or
other coating can but need not exhibit such ordering (e.g. it can
be amorphous, polycrystalline, or otherwise). In such instances,
the phrase "crystalline," "substantially crystalline,"
"substantially monocrystalline," or "monocrystalline" refers to the
central core of the nanostructure (excluding the coating layers or
shells). The terms "crystalline" or "substantially crystalline" as
used herein are intended to also encompass structures comprising
various defects, stacking faults, atomic substitutions, and the
like, as long as the structure exhibits substantial long range
ordering (e.g., order over at least about 80% of the length of at
least one axis of the nanostructure or its core). In addition, it
will be appreciated that the interface between a core and the
outside of a nanostructure or between a core and an adjacent shell
or between a shell and a second adjacent shell may contain
non-crystalline regions and may even be amorphous. This does not
prevent the nanostructure from being crystalline or substantially
crystalline as defined herein.
[0147] The term "monocrystalline" when used with respect to a
nanostructure indicates that the nanostructure is substantially
crystalline and comprises substantially a single crystal. When used
with respect to a nanostructure comprising a core and one or more
shells, "monocrystalline" indicates that the core is substantially
crystalline and comprises substantially a single crystal.
[0148] A "nanocrystal" is a nanostructure that is substantially
monocrystalline. A nanocrystal thus has at least one region or
characteristic dimension with a dimension of less than about 500
nm. In some embodiments, the nanocrystal has a dimension of less
than about 200 nm, less than about 100 nm, less than about 50 nm,
less than about 20 nm, or less than about 10 nm. The term
"nanocrystal" is intended to encompass substantially
monocrystalline nanostructures comprising various defects, stacking
faults, atomic substitutions, and the like, as well as
substantially monocrystalline nanostructures without such defects,
faults, or substitutions. In the case of nanocrystal
heterostructures comprising a core and one or more shells, the core
of the nanocrystal is typically substantially monocrystalline, but
the shell(s) need not be. In some embodiments, each of the three
dimensions of the nanocrystal has a dimension of less than about
500 nm, less than about 200 nm, less than about 100 nm, less than
about 50 nm, less than about 20 nm, or less than about 10 nm.
[0149] The term "quantum dot" (or "dot") refers to a nanocrystal
that exhibits quantum confinement or exciton confinement. Quantum
dots can be substantially homogenous in material properties, or in
certain embodiments, can be heterogeneous, e.g., including a core
and at least one shell. The optical properties of quantum dots can
be influenced by their particle size, chemical composition, and/or
surface composition, and can be determined by suitable optical
testing available in the art. The ability to tailor the nanocrystal
size, e.g., in the range between about 1 nm and about 15 nm,
enables photoemission coverage in the entire optical spectrum to
offer great versatility in color rendering.
[0150] A "ligand" is a molecule capable of interacting (whether
weakly or strongly) with one or more faces of a nanostructure,
e.g., through covalent, ionic, van der Waals, or other molecular
interactions with the surface of the nanostructure.
[0151] "Photoluminescence quantum yield" is the ratio of photons
emitted to photons absorbed, e.g., by a nanostructure or population
of nanostructures. As known in the art, quantum yield is typically
determined by a comparative method using well-characterized
standard samples with known quantum yield values.
[0152] "Peak emission wavelength" (PWL) is the wavelength where the
radiometric emission spectrum of the light source reaches its
maximum.
[0153] As used herein, the term "shell" refers to material
deposited onto the core or onto previously deposited shells of the
same or different composition and that result from a single act of
deposition of the shell material. The exact shell thickness depends
on the material as well as the precursor input and conversion and
can be reported in nanometers or monolayers. As used herein,
"target shell thickness" refers to the intended shell thickness
used for calculation of the required precursor amount. As used
herein, "actual shell thickness" refers to the actually deposited
amount of shell material after the synthesis and can be measured by
methods known in the art. By way of example, actual shell thickness
can be measured by comparing particle diameters determined from
transmission electron microscopy (TEM) images of nanocrystals
before and after a shell synthesis.
[0154] As used herein, the term "monolayer" is a measurement unit
of shell thickness derived from the bulk crystal structure of the
shell material as the closest distance between relevant lattice
planes. By way of example, for cubic lattice structures the
thickness of one monolayer is determined as the distance between
adjacent lattice planes in the [111] direction. By way of example,
one monolayer of cubic ZnSe corresponds to 0.328 nm and one
monolayer of cubic ZnS corresponds to 0.31 nm thickness. The
thickness of a monolayer of alloyed materials can be determined
from the alloy composition through Vegard's law.
[0155] As used herein, the term "full width at half-maximum" (FWHM)
is a measure of the size distribution of quantum dots. The emission
spectra of quantum dots generally have the shape of a Gaussian
curve. The width of the Gaussian curve is defined as the FWHM and
gives an idea of the size distribution of the particles. A smaller
FWHM corresponds to a narrower quantum dot nanocrystal size
distribution. FWHM is also dependent upon the emission wavelength
maximum.
[0156] As used herein, the term "external quantum efficiency" (EQE)
is a ratio of the number of photons emitted from a light emitting
diode (LED) to the number of electrons passing through the device.
The EQE measures how efficiently a LED converts electrons to
photons and allows them to escape. EQE can be measured using the
formula:
EQE=[injection efficiency].times.[solid-state quantum
yield].times.[extraction efficiency]
where: [0157] injection efficiency=the proportion of electrons
passing through the device that are injected into the active
region; [0158] solid-state quantum yield=the proportion of all
electron-hole recombinations in the active region that are
radiative and thus, produce photons; and [0159] extraction
efficiency=the proportion of photons generated in the active region
that escape from the device.
[0160] Unless clearly indicated otherwise, ranges listed herein are
inclusive.
[0161] A variety of additional terms are defined or otherwise
characterized herein.
Production of Nanostructures
[0162] Methods for colloidal synthesis of a variety of
nanostructures are known in the art. Such methods include
techniques for controlling nanostructure growth, e.g., to control
the size and/or shape distribution of the resulting
nanostructures.
[0163] In a typical colloidal synthesis, semiconductor
nanostructures are produced by rapidly injecting precursors that
undergo pyrolysis into a hot solution (e.g., hot solvent and/or
surfactant). The precursors can be injected simultaneously or
sequentially. The precursors rapidly react to form nuclei.
Nanostructure growth occurs through monomer addition to the
nuclei.
[0164] Surfactant molecules interact with the surface of the
nanostructure. At the growth temperature, the surfactant molecules
rapidly adsorb and desorb from the nanostructure surface,
permitting the addition and/or removal of atoms from the
nanostructure while suppressing aggregation of the growing
nanostructures. In general, a surfactant that coordinates weakly to
the nanostructure surface permits rapid growth of the
nanostructure, while a surfactant that binds more strongly to the
nanostructure surface results in slower nanostructure growth. The
surfactant can also interact with one (or more) of the precursors
to slow nanostructure growth.
[0165] Nanostructure growth in the presence of a single surfactant
typically results in spherical nanostructures. Using a mixture of
two or more surfactants, however, permits growth to be controlled
such that non-spherical nanostructures can be produced, if, for
example, the two (or more) surfactants adsorb differently to
different crystallographic faces of the growing nanostructure.
[0166] A number of parameters are thus known to affect
nanostructure growth and can be manipulated, independently or in
combination, to control the size and/or shape distribution of the
resulting nanostructures. These include, e.g., temperature
(nucleation and/or growth), precursor composition, time-dependent
precursor concentration, ratio of the precursors to each other,
surfactant composition, number of surfactants, and ratio of
surfactant(s) to each other and/or to the precursors.
[0167] Synthesis of Group II-VI nanostructures has been described,
e.g., in U.S. Pat. Nos. 6,225,198, 6,322,901, 6,207,229, 6,607,829,
7,060,243, 7,374,824, 6,861,155, 7,125,605, 7,566,476, 8,158,193,
and 8,101,234 and U.S. Patent Appl. Publication Nos. 2011/0262752
and 2011/0263062.
[0168] Although Group II-VI nanostructures such as CdSe/CdS/ZnS
core/shell quantum dots can exhibit desirable luminescence
behavior, as noted above, issues such as the toxicity of cadmium
limit the applications for which such nanostructures can be used.
Less toxic alternatives with favorable luminescence properties are
thus highly desirable.
[0169] In some embodiments, the nanostructures are free from
cadmium. As used herein, the term "free of cadmium" is intended
that the nanostructures contain less than 100 ppm by weight of
cadmium. The Restriction of Hazardous Substances (RoHS) compliance
definition requires that there must be no more than 0.01% (100 ppm)
by weight of cadmium in the raw homogeneous precursor materials.
The cadmium level in the Cd-free nanostructures of the present
invention is limited by the trace metal concentration in the
precursor materials. The trace metal (including cadmium)
concentration in the precursor materials for the Cd-free
nanostructures, is measured by inductively coupled plasma mass
spectroscopy (ICP-MS) analysis, and are on the parts per billion
(ppb) level. In some embodiments, nanostructures that are "free of
cadmium" contain less than about 50 ppm, less than about 20 ppm,
less than about 10 ppm, or less than about 1 ppm of cadmium.
Production of the ZnSe.sub.1-xTe.sub.x Core
[0170] Using density function theory (DFT) calculations, it is
predicted that the localization of Te atoms in the center of a ZnSe
core would result in a red shift in the observed emission spectra
while at the same time would maintain a type I overlap between the
electron and hole wave functions in the conduction and valence
bands. Type I overlap occurs in nanocrystals in which the
exciton-exciton interaction is attractive and hence the interaction
energy is negative. Piryatinski, A., et al., Nano Letters
7(1):108-115 (2007). On the other hand, by separating electrons and
holes spatially, one can increase the repulsive component of the
interaction energy, which can reverse the sign of the interaction
energy. In the case of strongly confined type II nanocrystals, this
strategy can lead not only to overall exciton-exciton repulsion but
also to large magnitudes of interaction energies, which can be
produced because of very small separation between interacting
charges.
[0171] It is believed that variation of the location and number of
Te atoms across the quantum dot core would result in peak
broadening. Trioctylphosphine telluride is known to decompose to
elemental Te, which is only slowly reduced to Te.sup.2-. See U.S.
Pat. No. 8,637,082. This reaction is not matched to that between
diethylzinc and trioctylphosphine selenide and results in low and
poorly controlled incorporation of Te atoms into ZnSe. Improved
ZnTe nanomaterials resulted from the use of strong reducing agents
in conjunction with trioctylphosphine telluride to promote the
formation of Te.sup.2-. See Zhang, J., et al., J. Phys. Chem. C.
112(14):5454-5458 (2008) which describes the use of zinc
carboxylates to prevent the formation of elemental zinc.
[0172] A conventional procedure for preparation of ZnSe cores
involves reduction of trioctylphosphine telluride with superhydride
in an oleylamine solution which forms a purple solution. The purple
solution is mixed with one equivalent of zinc carboxylate dissolved
in trioctylphosphine which results in the formation of a colorless
milky mixture that is still of sufficiently low viscosity for rapid
injection. This milky mixture is co-injected with diethylzinc into
trioctylphosphine selenide (at a level of 8 mole percentage
telluride). After the cores are grown and washed, the cores are
coated with a shell as described in U.S. Patent Appl. Publication
No. 2017/066965, which is incorporated herein by reference in its
entirety.
[0173] In some embodiments, the nanostructure comprises a
ZnSe.sub.1-xTe.sub.x core, wherein 0<x<1, 0<x<0.5,
0<x<0.25, 0<x<0.1, 0<x<0.05, 0<x<0.02,
0<x<0.01, 0.01<x<0.5, 0.01<x<0.25,
0.01<x<0.1, 0.01<x<0.05, 0.01<x<0.02,
0.02<x<0.5, 0.02<x<0.25, 0.02<x<0.1,
0.02<x<0.05, 0.05<x<0.5, 0.05<x<0.25,
0.05<x<0.1, 0.1<x<0.5, 0.1<x<0.25, or
0.5<x<0.25.
[0174] The diameter of the ZnSe.sub.1-xTe.sub.x core can be
controlled by varying the amount of precursors provided. The
diameter of the ZnSe.sub.1-xTe.sub.x core can be determined using
techniques known to those of skill in the art. In some embodiments,
the diameter of the ZnSe.sub.1-xTe.sub.x core is determined using
transmission electron microscopy (TEM).
[0175] In some embodiments, each ZnSe.sub.1-xTe.sub.x core has a
diameter of between about 1.0 nm and about 7.0 nm, about 1.0 nm and
about 6.0 nm, about 1.0 nm and about 5.0 nm, about 1.0 nm and about
4.0 nm, about 1.0 nm and about 3.0 nm, about 1.0 nm and about 2.0
nm, about 2.0 nm and about 7.0 nm, about 2.0 nm and about 6.0 nm,
about 2.0 nm and about 5.0 nm, about 2.0 nm and about 4.0 nm, about
2.0 nm and about 3.0 nm, about 3.0 nm and about 7.0 nm, about 3.0
nm and about 6.0 nm, about 3.0 nm and about 5.0 nm, about 3.0 nm
and about 4.0 nm, about 4.0 nm and about 7.0 nm, about 4.0 nm and
about 6.0 nm, about 4.0 nm and about 5.0 nm, about 5.0 nm and about
7.0 nm, about 5.0 nm and about 6.0 nm, or about 6.0 nm and about
7.0 nm. In some embodiments, the ZnSe.sub.1-xTe.sub.x core has a
diameter of between about 3.0 nm and about 5.0 nm.
[0176] The present disclosure also provides a method of producing a
ZnSe.sub.1-xTe.sub.x nanocrystal comprising:
[0177] (a) admixing a tellurium source, at least one ligand, and a
reducing agent to produce a reaction mixture;
[0178] (b) contacting the reaction mixture obtained in (a) with a
solution comprising at least one ligand, zinc fluoride, and a
selenium source; and
[0179] (c) contacting the reaction mixture obtained in (b) with a
zinc source; to provide a ZnSe.sub.1-xTe.sub.x nanocrystal.
[0180] In some embodiments, the present invention provides a method
of producing a ZnSe.sub.1-xTe.sub.x nanocrystal comprising:
[0181] (a) admixing a selenium source and at least one ligand to
produce a reaction mixture;
[0182] (b) contacting the reaction mixture obtained in (a) with a
solution comprising a tellurium source, a reducing agent, and a
zinc carboxylate; and
[0183] (c) contacting the reaction mixture obtained in (b) with a
zinc source; to provide a ZnSe.sub.1-xTe.sub.x nanocrystal.
[0184] In some embodiments, the present invention provides a method
of producing a ZnSe.sub.1-xTe.sub.x nanocrystal comprising:
[0185] (a) admixing a selenium source and at least one ligand to
produce a reaction mixture;
[0186] (b) contacting the reaction mixture obtained in (a) with a
solution comprising a tellurium source, a reducing agent, and a
zinc carboxylate; and
[0187] (c) contacting the reaction mixture obtained in (b) with a
zinc source;
[0188] (d) contacting the reaction mixture in (c) with a zinc
source and a selenium source; to provide a ZnSe.sub.1-xTe.sub.x
nanocrystal.
[0189] In some embodiments, the selenium source is selected from
trioctylphosphine selenide, tri(n-butyl)phosphine selenide,
tri(sec-butyl)phosphine selenide, tri(tert-butyl)phosphine
selenide, trimethylphosphine selenide, triphenylphosphine selenide,
diphenylphosphine selenide, phenylphosphine selenide,
cyclohexylphosphine selenide, octaselenol, dodecaselenol,
selenophenol, elemental selenium, hydrogen selenide,
bis(trimethylsilyl) selenide, and mixtures thereof. In some
embodiments, the selenium source is trioctylphosphine selenide
(TOPSe).
[0190] In some embodiments, the ZnSe.sub.1-xTe.sub.x core is
synthesized in the presence of at least one nanostructure ligand.
Ligands can, e.g., enhance the miscibility of nanostructures in
solvents or polymers (allowing the nanostructures to be distributed
throughout a composition such that the nanostructures do not
aggregate together), increase quantum yield of nanostructures,
and/or preserve nanostructure luminescence (e.g., when the
nanostructures are incorporated into a matrix). In some
embodiments, the ligand(s) for the core synthesis and for the shell
synthesis are the same. In some embodiments, the ligand(s) for the
core synthesis and for the shell synthesis are different. Following
synthesis, any ligand on the surface of the nanostructures can be
exchanged for a different ligand with other desirable properties.
Examples of ligands are disclosed in U.S. Patent Application
Publication Nos. 2005/0205849, 2008/0105855, 2008/0118755,
2009/0065764, 2010/0140551, 2013/0345458, 2014/0151600,
2014/0264189, and 2014/0001405.
[0191] In some embodiments, ligands suitable for the synthesis of
nanostructure cores, including ZnSe.sub.1-xTe.sub.x cores, are
known by those of skill in the art. In some embodiments, the ligand
is a fatty acid selected from lauric acid, caproic acid, myristic
acid, palmitic acid, stearic acid, and oleic acid. In some
embodiments, the ligand is an organic phosphine or an organic
phosphine oxide selected from trioctylphosphine oxide (TOPO),
trioctylphosphine (TOP), diphenylphosphine (DPP),
triphenylphosphine oxide, and tributylphosphine oxide. In some
embodiments, the ligand is an amine selected from dodecylamine,
oleylamine, hexadecylamine, and octadecylamine. In some
embodiments, the ligand is trioctylphosphine (TOP). In some
embodiments, the ligand is oleylamine.
[0192] In some embodiments, the core is produced in the presence of
a mixture of ligands. In some embodiments, the core is produced in
the presence of a mixture comprising 2, 3, 4, 5, or 6 different
ligands. In some embodiments, the core is produced in the presence
of a mixture comprising 3 different ligands. In some embodiments,
the mixture of ligands comprises oleylamine, diphenylphosphine, and
trioctylphosphine.
[0193] In some embodiments, a selenium source and a ligand are
admixed in (a) at a reaction temperature between about 250.degree.
C. and about 350.degree. C., about 250.degree. C. and about
320.degree. C., about 250.degree. C. and about 300.degree. C.,
about 250.degree. C. and about 290.degree. C., about 250.degree. C.
and about 280.degree. C., about 250.degree. C. and about
270.degree. C., about 270.degree. C. and about 350.degree. C.,
about 270.degree. C. and about 320.degree. C., about 270.degree. C.
and about 300.degree. C., about 270.degree. C. and about
290.degree. C., about 270.degree. C. and about 280.degree. C.,
about 280.degree. C. and about 350.degree. C., about 280.degree. C.
and about 320.degree. C., about 280.degree. C. and about
300.degree. C., about 280.degree. C. and about 290.degree. C.,
about 290.degree. C. and about 350.degree. C., about 290.degree. C.
and about 320.degree. C., about 290.degree. C. and about
300.degree. C., about 300.degree. C. and about 350.degree. C.,
about 300.degree. C. and about 320.degree. C., or about 320.degree.
C. and about 350.degree. C. In some embodiments, a selenium source
and a ligand are admixed in (a) at a reaction temperature of about
300.degree. C.
[0194] In some embodiments, the reaction mixture after admixing a
selenium source and a ligand in (a) is maintained at an elevated
temperature for between about 2 and about 20 minutes, about 2 and
about 15 minutes, about 2 and about 10 minutes, about 2 and about 8
minutes, about 2 and about 5 minutes, about 5 and about 20 minutes,
about 5 and about 15 minutes, about 5 and about 10 minutes, about 5
and about 8 minutes, about 8 and about 20 minutes, about 8 and
about 15 minutes, about 8 and about 10 minutes, about 10 and about
20 minutes, about 10 and about 15 minutes, or about 15 and about 20
minutes.
[0195] In some embodiments, the solution comprising a tellurium
source, a reducing agent, and a zinc carboxylate in (b) is prepared
separately. In some embodiments, the solution comprising a
tellurium source, a reducing agent, and a zinc carboxylate in (b)
is prepared in situ.
[0196] In some embodiments, the solution comprising a tellurium
source, a reducing agent, and a zinc carboxylate in (b) is prepared
separately. In some embodiments, the method for preparing the
tellurium solution comprises:
[0197] (a) admixing a tellurium source and a ligand to produce a
reaction mixture;
[0198] (b) contacting the reaction mixture in (a) with a reducing
agent; and
[0199] (c) contacting the reaction mixture in (b) with a zinc
carboxylate; to produce a tellurium solution.
[0200] In some embodiments, the tellurium source is selected from
trioctylphosphine telluride, tri(n-butyl)phosphine telluride,
trimethylphosphine telluride, triphenylphosphine telluride,
tricyclohexylphosphine telluride, elemental tellurium, hydrogen
telluride, bis(trimethylsilyl) telluride, and mixtures thereof. In
some embodiments, the tellurium source is trioctylphosphine
telluride (TOPTe).
[0201] In some embodiments, the reducing agent is selected from
diborane, sodium hydride, sodium borohydride, lithium borohydride,
sodium cyanoborohydride, calcium hydride, lithium hydride, lithium
aluminum hydride, diisobutylaluminum hydride, sodium
triethylborohydride, and lithium triethylborohydride. In some
embodiments, the reducing agent is lithium triethylborohydride.
[0202] In some embodiments, the zinc carboxylate is produced by
reacting a zinc salt and a carboxylic acid.
[0203] In some embodiments, the zinc salt is selected from zinc
acetate, zinc fluoride, zinc chloride, zinc bromide, zinc iodide,
zinc nitrate, zinc triflate, zinc tosylate, zinc mesylate, zinc
oxide, zinc sulfate, zinc acetylacetonate, zinc
toluene-3,4-dithiolate, zinc p-toluenesulfonate, zinc
diethyldithiocarbamate, zinc dibenzyldithiocarbamate, and mixtures
thereof.
[0204] In some embodiments, the carboxylic acid is selected from
acetic acid, propionic acid, butyric acid, valeric acid, caproic
acid, heptanoic acid, caprylic acid, capric acid, undecanoic acid,
lauric acid, myristic acid, palmitic acid, stearic acid, behenic
acid, acrylic acid, methacrylic acid, but-2-enoic acid, but-3-enoic
acid, pent-2-enoic acid, pent-4-enoic acid, hex-2-enoic acid,
hex-3-enoic acid, hex-4-enoic acid, hex-5-enoic acid, hept-6-enoic
acid, oct-2-enoic acid, dec-2-enoic acid, undec-10-enoic acid,
dodec-5-enoic acid, oleic acid, gadoleic acid, erucic acid,
linoleic acid, .alpha.-linolenic acid, calendic acid, eicosadienoic
acid, eicosatrienoic acid, arachidonic acid, stearidonic acid,
benzoic acid, para-toluic acid, ortho-toluic acid, meta-toluic
acid, hydrocinnamic acid, naphthenic acid, cinnamic acid,
para-toluenesulfonic acid, and mixtures thereof.
[0205] In some embodiments, the zinc carboxylate is zinc stearate
or zinc oleate. In some embodiments, the zinc carboxylate is zinc
oleate.
[0206] In some embodiments, the solution comprising a tellurium
source, a reducing agent, and a zinc carboxylate in (b) are added
to the reaction mixture at a reaction temperature between about
250.degree. C. and about 350.degree. C., about 250.degree. C. and
about 320.degree. C., about 250.degree. C. and about 300.degree.
C., about 250.degree. C. and about 290.degree. C., about
250.degree. C. and about 280.degree. C., about 250.degree. C. and
about 270.degree. C., about 270.degree. C. and about 350.degree.
C., about 270.degree. C. and about 320.degree. C., about
270.degree. C. and about 300.degree. C., about 270.degree. C. and
about 290.degree. C., about 270.degree. C. and about 280.degree.
C., about 280.degree. C. and about 350.degree. C., about
280.degree. C. and about 320.degree. C., about 280.degree. C. and
about 300.degree. C., about 280.degree. C. and about 290.degree.
C., about 290.degree. C. and about 350.degree. C., about
290.degree. C. and about 320.degree. C., about 290.degree. C. and
about 300.degree. C., about 300.degree. C. and about 350.degree.
C., about 300.degree. C. and about 320.degree. C., or about
320.degree. C. and about 350.degree. C. In some embodiments, the
solution comprising a tellurium source, a reducing agent, and a
zinc carboxylate in (b) are added to the reaction mixture at a
reaction temperature of about 300.degree. C.
[0207] In some embodiments, the reaction mixture--after addition of
a solution comprising a tellurium source, a reducing agent, and a
zinc carboxylate in (b)--is contacted with a zinc source in
(c).
[0208] In some embodiments, the zinc source in (c) is added to the
reaction mixture between about 1 second and about 5 minutes, about
1 second and about 3 minutes, about 1 second and about 1 minute,
about 1 second and about 30 seconds, about 1 second and about 10
seconds, about 1 second and about 5 seconds, about 5 seconds and
about 5 minutes, about 5 seconds and about 3 minutes, about 5
seconds and about 1 minute, about 5 seconds and about 30 seconds,
about 5 seconds and about 10 seconds, about 10 seconds and about 5
minutes, about 10 seconds and about 3 minutes, about 10 seconds and
about 1 minute, about 10 seconds and about 30 seconds, about 30
seconds and about 5 minutes, about 30 seconds and about 3 minutes,
about 30 seconds and about 1 minute, about 1 minute and about 5
minutes, about 1 minute and about 3 minutes, or about 3 minutes and
about 5 minutes after addition of the solution in (b) comprising a
tellurium source, a reducing agent, and a zinc carboxylate. In some
embodiments, the zinc source in (c) is added to the reaction
mixture between about 1 second and 5 seconds after addition of the
solution in (b) comprising a tellurium source, a reducing agent,
and a zinc carboxylate.
[0209] In some embodiments, the zinc source is added to the
reaction mixture in (c) at a reaction temperature between about
250.degree. C. and about 350.degree. C., about 250.degree. C. and
about 320.degree. C., about 250.degree. C. and about 300.degree.
C., about 250.degree. C. and about 290.degree. C., about
250.degree. C. and about 280.degree. C., about 250.degree. C. and
about 270.degree. C., about 270.degree. C. and about 350.degree.
C., about 270.degree. C. and about 320.degree. C., about
270.degree. C. and about 300.degree. C., about 270.degree. C. and
about 290.degree. C., about 270.degree. C. and about 280.degree.
C., about 280.degree. C. and about 350.degree. C., about
280.degree. C. and about 320.degree. C., about 280.degree. C. and
about 300.degree. C., about 280.degree. C. and about 290.degree.
C., about 290.degree. C. and about 350.degree. C., about
290.degree. C. and about 320.degree. C., about 290.degree. C. and
about 300.degree. C., about 300.degree. C. and about 350.degree.
C., about 300.degree. C. and about 320.degree. C., or about
320.degree. C. and about 350.degree. C. In some embodiments, a zinc
source in (c) added to the reaction mixture at a reaction
temperature of about 300.degree. C.
[0210] In some embodiments, the zinc source in (c) is a dialkyl
zinc compound. In some embodiments, the zinc source is diethylzinc,
dimethylzinc, diphenylzinc, zinc acetate, zinc acetylacetonate,
zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc
carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide,
zinc perchlorate, or zinc sulfate. In some embodiments, the zinc
source is diethylzinc or dimethylzinc. In some embodiments, the
zinc source is diethylzinc.
[0211] In some embodiments, the mole percentage of tellurium source
to zinc source is between about 1% and about 20%, about 1% and
about 15%, about 1% and about 10%, about 1% and about 8%, about 1%
and about 6%, about 1% and about 4%, about 1% and about 2%, about
2% and about 20%, about 2% and about 15%, about 2% and about 10%,
about 2% and about 8%, about 2% and about 6%, about 2% and about
4%, about 4% and about 20%, about 4% and about 15%, about 4% and
about 10%, about 4% and about 8%, about 4% and about 6%, about 6%
and about 20%, about 6% and about 15%, about 6% and about 10%,
about 6% and about 8%, about 8% and about 20%, about 8% and about
15%, about 8% and about 10%, about 10% and about 20%, about 10% and
about 15%, or about 15% and about 20%. In some embodiments, the
mole percentage of tellurium source to zinc source is between about
6% and about 10%. In some embodiments, the mole percentage of
tellurium source to zinc source is about 8%.
[0212] In some embodiments, the reaction mixture--after addition of
a zinc source in (c)--is contacted with a zinc source and a
selenium source. In some embodiments, the zinc source and the
selenium source are added in (d) to the reaction mixture at a
reaction temperature between about 250.degree. C. and about
350.degree. C., about 250.degree. C. and about 320.degree. C.,
about 250.degree. C. and about 300.degree. C., about 250.degree. C.
and about 290.degree. C., about 250.degree. C. and about
280.degree. C., about 250.degree. C. and about 270.degree. C.,
about 270.degree. C. and about 350.degree. C., about 270.degree. C.
and about 320.degree. C., about 270.degree. C. and about
300.degree. C., about 270.degree. C. and about 290.degree. C.,
about 270.degree. C. and about 280.degree. C., about 280.degree. C.
and about 350.degree. C., about 280.degree. C. and about
320.degree. C., about 280.degree. C. and about 300.degree. C.,
about 280.degree. C. and about 290.degree. C., about 290.degree. C.
and about 350.degree. C., about 290.degree. C. and about
320.degree. C., about 290.degree. C. and about 300.degree. C.,
about 300.degree. C. and about 350.degree. C., about 300.degree. C.
and about 320.degree. C., or about 320.degree. C. and about
350.degree. C. In some embodiments, a zinc source and a selenium
source in (d) are added to the reaction mixture at a reaction
temperature of about 280.degree. C.
[0213] In some embodiments, the zinc source and the selenium source
are added in (d) over a period of between about 2 and about 120
minutes, about 2 and about 60 minutes, about 2 and about 30
minutes, about 2 and about 20 minutes, about 2 and about 15
minutes, about 2 and about 10 minutes, about 2 and about 8 minutes,
about 2 and about 5 minutes, about 5 and about 120 minutes, about 5
and about 60 minutes, about 5 and about 30 minutes, about 5 and
about 20 minutes, about 5 and about 15 minutes, about 5 and about
10 minutes, about 5 and about 8 minutes, about 8 and about 120
minutes, about 8 and about 60 minutes, about 8 and about 30
minutes, about 8 and about 20 minutes, about 8 and about 15
minutes, about 8 and about 10 minutes, about 10 and about 120
minutes, about 10 and about 60 minutes, about 10 and about 30
minutes, about 10 and about 20 minutes, about 10 and about 15
minutes, about 15 and about 120 minutes, about 15 and about 60
minutes, about 15 and about 30 minutes, about 15 and about 20
minutes, about 20 and about 120 minutes, about 20 and about 60
minutes, about 20 and about 30 minutes, about 30 and about 120
minutes, about 30 and about 60 minutes, or about 60 and about 120
minutes. In some embodiments, the zinc source and the selenium
source are added over a period of about 20 minutes and about 30
minutes.
[0214] In some embodiments, the reaction mixture--after addition of
a zinc source and a selenium source in (d)--is maintained at an
elevated temperature for between about 2 and about 20 minutes,
about 2 and about 15 minutes, about 2 and about 10 minutes, about 2
and about 8 minutes, about 2 and about 5 minutes, about 5 and about
20 minutes, about 5 and about 15 minutes, about 5 and about 10
minutes, about 5 and about 8 minutes, about 8 and about 20 minutes,
about 8 and about 15 minutes, about 8 and about 10 minutes, about
10 and about 20 minutes, about 10 and about 15 minutes, or about 15
and about 20 minutes. In some embodiments, the reaction
mixture--after addition of a zinc source and a selenium source in
(d)--is maintained at an elevated temperature for between about 2
and about 10 minutes.
[0215] To prevent precipitation of the ZnSe.sub.1-xTe.sub.x cores
as additional precursors are added, additional ligand can be added
during the growth phase. If too much ligand is added during the
initial nucleation phase, the concentration of the zinc source,
selenium source, and tellurium source would be too low and would
prevent effective nucleation. Therefore, the ligand is added slowly
throughout the growth phase. In some embodiments, the additional
ligand is oleylamine.
[0216] After the ZnSe.sub.1-xTe.sub.x cores reach the desired
thickness and diameter, they can be cooled. In some embodiments,
the ZnSe.sub.1-xTe.sub.x cores are cooled to room temperature. In
some embodiments, an organic solvent is added to dilute the
reaction mixture comprising the ZnSe.sub.1-xTe.sub.x cores.
[0217] In some embodiments, the organic solvent is hexane, pentane,
toluene, benzene, diethylether, acetone, ethyl acetate,
dichloromethane (methylene chloride), chloroform,
dimethylformamide, or N-methylpyrrolidinone. In some embodiments,
the organic solvent is toluene.
[0218] In some embodiments, the ZnSe.sub.1-xTe.sub.x cores are
isolated. In some embodiments, the ZnSe.sub.1-xTe.sub.x cores are
isolated by precipitation of the ZnSe.sub.1-xTe.sub.x from solvent.
In some embodiments, the ZnSe.sub.1-xTe.sub.x cores are isolated by
precipitation with ethanol.
[0219] The size distribution of the ZnSe.sub.1-xTe.sub.x cores
prepared using the methods described herein can be relatively
narrow. In some embodiments, the photoluminescence spectrum of the
population or core/shell(s) nanostructures prepared using the
methods described herein have a full width at half-maximum of
between about 10 nm and about 30 nm, about 10 nm and about 25 nm,
about 10 nm and about 20 nm, about 10 nm and about 22 nm, about 10
nm and about 15 nm, about 15 nm and about 30 nm, about 15 nm and
about 25 nm, about 15 nm and about 22 nm, about 15 nm and about 20
nm, about 20 nm and about 30 nm, about 20 nm and about 25 nm, about
20 nm and about 22 nm, about 22 nm and about 30 nm, about 22 nm and
about 25 nm, or about 25 nm and about 30 nm. In some embodiments,
the photoluminescence spectrum of the population or
ZnSe.sub.1-xTe.sub.x cores prepared using the methods described
herein have a full width at half-maximum of between about 15 nm and
about 22 nm.
Production of a Shell
[0220] In some embodiments, the nanostructures of the present
invention include a core and at least one shell. In some
embodiments, the nanostructures of the present invention include a
core and at least two shells. The shell can, e.g., increase the
quantum yield and/or stability of the nanostructures. In some
embodiments, the core and the shell comprise different materials.
In some embodiments, the nanostructure comprises shells of
different shell material.
[0221] In some embodiments, a shell that comprises a mixture of
Group II and VI elements is deposited onto a core or a
core/shell(s) structure. In some embodiments, the shell deposited
is a mixture of at least two of a zinc source, a selenium source, a
sulfur source, and a tellurium source. In some embodiments, the
shell deposited is a mixture of two of a zinc source, a selenium
source, a sulfur source, and a tellurium source. In some
embodiments, the shell deposited is a mixture of three of a zinc
source, a selenium source, a sulfur source, and a tellurium source.
In some embodiments, the shell comprises zinc and sulfur; zinc and
selenium; zinc, sulfur, and selenium; zinc and tellurium; zinc,
tellurium, and sulfur; or zinc, tellurium, and selenium.
[0222] In some embodiments, a shell comprises more than one
monolayer of shell material. The number of monolayers is an average
for all the nanostructures; therefore, the number of monolayers in
a shell may be a fraction. In some embodiments, the number of
monolayers in a shell is between about 0.25 and about 10, about
0.25 and about 8, about 0.25 and about 7, about 0.25 and about 6,
about 0.25 and about 5, about 0.25 and about 4, about 0.25 and
about 3, about 0.25 and about 2, about 2 and about 10, about 2 and
about 8, about 2 and about 7, about 2 and about 6, about 2 and
about 5, about 2 and about 4, about 2 and about 3, about 3 and
about 10, about 3 and about 8, about 3 and about 7, about 3 and
about 6, about 3 and about 5, about 3 and about 4, about 4 and
about 10, about 4 and about 8, about 4 and about 7, about 4 and
about 6, about 4 and about 5, about 5 and about 10, about 5 and
about 8, about 5 and about 7, about 5 and about 6, about 6 and
about 10, about 6 and about 8, about 6 and about 7, about 7 and
about 10, about 7 and about 8, or about 8 and about 10. In some
embodiments, the shell comprises between about 3 and about 6
monolayers.
[0223] The thickness of the shell can be controlled by varying the
amount of precursor provided. For a given shell thickness, at least
one of the precursors is optionally provided in an amount whereby,
when a growth reaction is substantially complete, a shell of a
predetermined thickness is obtained. If more than one different
precursor is provided, either the amount of each precursor can be
limited or one of the precursors can be provided in a limiting
amount while the others are provided in excess.
[0224] The thickness of each shell can be determined using
techniques known to those of skill in the art. In some embodiments,
the thickness of each shell is determined by comparing the average
diameter of the nanostructure before and after the addition of each
shell. In some embodiments, the average diameter of the
nanostructure before and after the addition of each shell is
determined by transmission electron microscopy (TEM). In some
embodiments, each shell has a thickness of between about 0.05 nm
and about 3.5 nm, about 0.05 nm and about 2 nm, about 0.05 nm and
about 0.9 nm, about 0.05 nm and about 0.7 nm, about 0.05 nm and
about 0.5 nm, about 0.05 nm and about 0.3 nm, about 0.05 nm and
about 0.1 nm, about 0.1 nm and about 3.5 nm, about 0.1 nm and about
2 nm, about 0.1 nm and about 0.9 nm, about 0.1 nm and about 0.7 nm,
about 0.1 nm and about 0.5 nm, about 0.1 nm and about 0.3 nm, about
0.3 nm and about 3.5 nm, about 0.3 nm and about 2 nm, about 0.3 nm
and about 0.9 nm, about 0.3 nm and about 0.7 nm, about 0.3 nm and
about 0.5 nm, about 0.5 nm and about 3.5 nm, about 0.5 nm and about
2 nm, about 0.5 nm and about 0.9 nm, about 0.5 nm and about 0.7 nm,
about 0.7 nm and about 3.5 nm, about 0.7 nm and about 2 nm, about
0.7 nm and about 0.9 nm, about 0.9 nm and about 3.5 nm, about 0.9
nm and about 2 nm, or about 2 nm and about 3.5 nm.
[0225] In some embodiments, each shell is synthesized in the
presence of at least one nanostructure ligand. Ligands can, e.g.,
enhance the miscibility of nanostructures in solvents or polymers
(allowing the nanostructures to be distributed throughout a
composition such that the nanostructures do not aggregate
together), increase quantum yield of nanostructures, and/or
preserve nanostructure luminescence (e.g., when the nanostructures
are incorporated into a matrix). In some embodiments, the ligand(s)
for the core synthesis and for the shell synthesis are the same. In
some embodiments, the ligand(s) for the core synthesis and for the
shell synthesis are different. Following synthesis, any ligand on
the surface of the nanostructures can be exchanged for a different
ligand with other desirable properties. Examples of ligands are
disclosed in U.S. Pat. Nos. 7,572,395, 8,143,703, 8,425,803,
8,563,133, 8,916,064, 9,005,480, 9,139,770, and 9,169,435, and in
U.S. Patent Appl. Publication No. 2008/0118755.
[0226] Ligands suitable for the synthesis of a shell are known by
those of skill in the art. In some embodiments, the ligand is a
fatty acid selected from the group consisting of lauric acid,
caproic acid, caprylic acid, myristic acid, palmitic acid, stearic
acid, and oleic acid. In some embodiments, the ligand is an organic
phosphine or an organic phosphine oxide selected from
trioctylphosphine oxide (TOPO), trioctylphosphine (TOP),
diphenylphosphine (DPP), triphenylphosphine oxide, and
tributylphosphine oxide. In some embodiments, the ligand is an
amine selected from the group consisting of dodecylamine,
oleylamine, hexadecylamine, dioctylamine, and octadecylamine. In
some embodiments, the ligand is trioctylphosphine oxide,
trioctylphosphine, or lauric acid.
[0227] In some embodiments, each shell is produced in the presence
of a mixture of ligands. In some embodiments, each shell is
produced in the presence of a mixture comprising 2, 3, 4, 5, or 6
different ligands. In some embodiments, each shell is produced in
the presence of a mixture comprising 3 different ligands. In some
embodiments, the mixture of ligands comprises tributylphosphine
oxide, trioctylphosphine, and lauric acid.
[0228] In some embodiments, each shell is produced in the presence
of a solvent. In some embodiments, the solvent is selected from the
group consisting of 1-octadecene, 1-hexadecene, 1-eicosene,
eicosane, octadecane, hexadecane, tetradecane, squalene, squalane,
trioctylphosphine oxide, and dioctyl ether.
[0229] In some embodiments, a core or a core/shell(s) and shell
precursor are admixed at an temperature between about 20.degree. C.
and about 310.degree. C., about 20.degree. C. and about 280.degree.
C., about 20.degree. C. and about 250.degree. C., about 20.degree.
C. and about 200.degree. C., about 20.degree. C. and about
150.degree. C., about 20.degree. C. and about 100.degree. C., about
20.degree. C. and about 50.degree. C., about 50.degree. C. and
about 310.degree. C., about 50.degree. C. and about 280.degree. C.,
about 50.degree. C. and about 250.degree. C., about 50.degree. C.
and about 200.degree. C., about 50.degree. C. and about 150.degree.
C., about 50.degree. C. and about 100.degree. C., about 100.degree.
C. and about 310.degree. C., about 100.degree. C. and about
280.degree. C., about 100.degree. C. and about 250.degree. C.,
about 100.degree. C. and about 200.degree. C., about 100.degree. C.
and about 150.degree. C., about 150.degree. C. and about
310.degree. C., about 150.degree. C. and about 280.degree. C.,
about 150.degree. C. and about 250.degree. C., about 150.degree. C.
and about 200.degree. C., about 200.degree. C. and about
310.degree. C., about 200.degree. C. and about 280.degree. C.,
about 200.degree. C. and about 250.degree. C., about 250.degree. C.
and about 310.degree. C., about 250.degree. C. and about
280.degree. C., or about 280.degree. C. and about 310.degree.
C.
[0230] In some embodiments, after admixing a core or core/shell(s)
and shell precursor, the temperature of the reaction mixture is
increased to an elevated temperature between about 200.degree. C.
and about 310.degree. C., about 200.degree. C. and about
280.degree. C., about 200.degree. C. and about 250.degree. C.,
about 200.degree. C. and about 220.degree. C., about 220.degree. C.
and about 310.degree. C., about 220.degree. C. and about
280.degree. C., about 220.degree. C. and about 250.degree. C.,
about 250.degree. C. and about 310.degree. C., about 250.degree. C.
and about 280.degree. C., or about 280.degree. C. and about
310.degree. C.
[0231] In some embodiments, after admixing a core or core/shell(s)
and shell precursor, the time for the temperature to reach the
elevated temperature is between about 2 and about 240 minutes,
about 2 and about 200 minutes, about 2 and about 100 minutes, about
2 and about 60 minutes, about 2 and about 40 minutes, about 5 and
about 240 minutes, about 5 and about 200 minutes, about 5 and about
100 minutes, about 5 and about 60 minutes, about 5 and about 40
minutes, about 10 and about 240 minutes, about 10 and about 200
minutes, about 10 and about 100 minutes, about 10 and about 60
minutes, about 10 and about 40 minutes, about 40 and about 240
minutes, about 40 and about 200 minutes, about 40 and about 100
minutes, about 40 and about 60 minutes, about 60 and about 240
minutes, about 60 and about 200 minutes, about 60 and about 100
minutes, about 100 and about 240 minutes, about 100 and about 200
minutes, or about 200 and about 240 minutes.
[0232] In some embodiments, after admixing a core or core/shell(s)
and shell precursor, the temperature of the reaction mixture is
maintained at an elevated temperature for between 2 and about 240
minutes, about 2 and about 200 minutes, about 2 and about 100
minutes, about 2 and about 60 minutes, about 2 and about 40
minutes, about 5 and about 240 minutes, about 5 and about 200
minutes, about 5 and about 100 minutes, about 5 and about 60
minutes, about 5 and about 40 minutes, about 10 and about 240
minutes, about 10 and about 200 minutes, about 10 and about 100
minutes, about 10 and about 60 minutes, about 10 and about 40
minutes, about 40 and about 240 minutes, about 40 and about 200
minutes, about 40 and about 100 minutes, about 40 and about 60
minutes, about 60 and about 240 minutes, about 60 and about 200
minutes, about 60 and about 100 minutes, about 100 and about 240
minutes, about 100 and about 200 minutes, or about 200 and about
240 minutes.
[0233] In some embodiments, additional shells are produced by
further additions of shell material precursors that are added to
the reaction mixture followed by maintaining at an elevated
temperature. Typically, additional shell precursor is provided
after reaction of the previous shell is substantially complete
(e.g., when at least one of the previous precursors is depleted or
removed from the reaction or when no additional growth is
detectable). The further additions of precursor create additional
shells.
[0234] In some embodiments, the nanostructure is cooled before the
addition of additional shell material precursor to provide further
shells. In some embodiments, the nanostructure is maintained at an
elevated temperature before the addition of shell material
precursor to provide further shells.
[0235] After sufficient layers of shell have been added for the
nanostructure to reach the desired thickness and diameter, the
nanostructure can be cooled. In some embodiments, the core/shell(s)
nanostructures are cooled to room temperature. In some embodiments,
an organic solvent is added to dilute the reaction mixture
comprising the core/shell(s) nanostructures.
[0236] In some embodiments, the organic solvent used to dilute the
reaction mixture is ethanol, hexane, pentane, toluene, benzene,
diethylether, acetone, ethyl acetate, dichloromethane (methylene
chloride), chloroform, dimethylformamide, or N-methylpyrrolidinone.
In some embodiments, the organic solvent is toluene.
[0237] In some embodiments, core/shell(s) nanostructures are
isolated. In some embodiments, the core/shell(s) nanostructures are
isolated by precipitation using an organic solvent. In some
embodiments, the core/shell(s) nanostructures are isolated by
flocculation with ethanol.
[0238] The number of monolayers will determine the size of the
core/shell(s) nanostructures. The size of the core/shell(s)
nanostructures can be determined using techniques known to those of
skill in the art. In some embodiments, the size of the
core/shell(s) nanostructures is determined using TEM. In some
embodiments, the core/shell(s) nanostructures have an average
diameter of between about 1 nm and about 15 nm, about 1 nm and
about 10 nm, about 1 nm and about 9 nm, about 1 nm and about 8 nm,
about 1 nm and about 7 nm, about 1 nm and about 6 nm, about 1 nm
and about 5 nm, about 5 nm and about 15 nm, about 5 nm and about 10
nm, about 5 nm and about 9 nm, about 5 nm and about 8 nm, about 5
nm and about 7 nm, about 5 nm and about 6 nm, about 6 nm and about
15 nm, about 6 nm and about 10 nm, about 6 nm and about 9 nm, about
6 nm and about 8 nm, about 6 nm and about 7 nm, about 7 nm and
about 15 nm, about 7 nm and about 10 nm, about 7 nm and about 9 nm,
about 7 nm and about 8 nm, about 8 nm and about 15 nm, about 8 nm
and about 10 nm, about 8 nm and about 9 nm, about 9 nm and about 15
nm, about 9 nm and about 10 nm, or about 10 nm and about 15 nm.
[0239] In some embodiments, the core/shell(s) nanostructure is
subjected to an acid etching step before deposition of an
additional shell.
Production of a ZnSe Shell
[0240] In some embodiments, the shell deposited onto the core or
core/shell(s) nanostructure is a ZnSe shell.
[0241] In some embodiments, the shell precursors contacted with a
core or core/shell(s) nanostructure to prepare a ZnSe shell
comprise a zinc source and a selenium source.
[0242] In some embodiments, the zinc source is a dialkyl zinc
compound. In some embodiments, the zinc source is a zinc
carboxylate. In some embodiments, the zinc source is diethylzinc,
dimethylzinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc
bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc
cyanide, zinc nitrate, zinc oleate, zinc oxide, zinc peroxide, zinc
perchlorate, zinc sulfate, zinc hexanoate, zinc octanoate, zinc
laurate, zinc myristate, zinc palmitate, zinc stearate, zinc
dithiocarbamate, or mixtures thereof. In some embodiments, the zinc
source is zinc oleate, zinc hexanoate, zinc octanoate, zinc
laurate, zinc myristate, zinc palmitate, zinc stearate, zinc
dithiocarbamate, or mixtures thereof. In some embodiments, the zinc
source is zinc oleate.
[0243] In some embodiments, the selenium source is an
alkyl-substituted selenourea. In some embodiments, the selenium
source is a phosphine selenide. In some embodiments, the selenium
source is selected from trioctylphosphine selenide,
tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,
tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,
triphenylphosphine selenide, diphenylphosphine selenide,
phenylphosphine selenide, tricyclohexylphosphine selenide,
cyclohexylphosphine selenide, 1-octaneselenol, 1-dodecaneselenol,
selenophenol, elemental selenium, hydrogen selenide,
bis(trimethylsilyl) selenide, selenourea, and mixtures thereof. In
some embodiments, the selenium source is tri(n-butyl)phosphine
selenide, tri(sec-butyl)phosphine selenide, or
tri(tert-butyl)phosphine selenide. In some embodiments, the
selenium source is trioctylphosphine selenide.
[0244] In some embodiments, the molar ratio of core to zinc source
to prepare a ZnSe shell is between about 1:2 and about 1:1000,
about 1:2 and about 1:100, about 1:2 and about 1:50, about 1:2 and
about 1:25, about 1:2 and about 1:15, about 1:2 and about 1:10,
about 1:2 and about 1:5, about 1:5 and about 1:1000, about 1:5 and
about 1:100, about 1:5 and about 1:50, about 1:5 and about 1:25,
about 1:5 and about 1:15, about 1:5 and about 1:10, about 1:10 and
about 1:1000, about 1:10 and about 1:100, about 1:10 and about
1:50, about 1:10 and about 1:25, about 1:10 and about 1:15, about
1:15 and about 1:1000, about 1:15 and about 1:100, about 1:15 and
about 1:50, about 1:15 and about 1:25, about 1:25 and about 1:1000,
about 1:25 and about 1:100, about 1:25 and about 1:50, about 1:50
and about 1:1000, about 1:50 and about 1:100, or about 1:100 and
about 1:1000.
[0245] In some embodiments, the molar ratio of core to selenium
source to prepare a ZnSe shell is between about 1:2 and about
1:1000, about 1:2 and about 1:100, about 1:2 and about 1:50, about
1:2 and about 1:25, about 1:2 and about 1:15, about 1:2 and about
1:10, about 1:2 and about 1:5, about 1:5 and about 1:1000, about
1:5 and about 1:100, about 1:5 and about 1:50, about 1:5 and about
1:25, about 1:5 and about 1:15, about 1:5 and about 1:10, about
1:10 and about 1:1000, about 1:10 and about 1:100, about 1:10 and
about 1:50, about 1:10 and about 1:25, about 1:10 and about 1:15,
about 1:15 and about 1:1000, about 1:15 and about 1:100, about 1:15
and about 1:50, about 1:15 and about 1:25, about 1:25 and about
1:1000, about 1:25 and about 1:100, about 1:25 and about 1:50,
about 1:50 and about 1:1000, about 1:50 and about 1:100, or about
1:100 and about 1:1000.
[0246] In some embodiments, the number of monolayers in a ZnSe
shell is between about 0.25 and about 10, about 0.25 and about 8,
about 0.25 and about 7, about 0.25 and about 6, about 0.25 and
about 5, about 0.25 and about 4, about 0.25 and about 3, about 0.25
and about 2, about 2 and about 10, about 2 and about 8, about 2 and
about 7, about 2 and about 6, about 2 and about 5, about 2 and
about 4, about 2 and about 3, about 3 and about 10, about 3 and
about 8, about 3 and about 7, about 3 and about 6, about 3 and
about 5, about 3 and about 4, about 4 and about 10, about 4 and
about 8, about 4 and about 7, about 4 and about 6, about 4 and
about 5, about 5 and about 10, about 5 and about 8, about 5 and
about 7, about 5 and about 6, about 6 and about 10, about 6 and
about 8, about 6 and about 7, about 7 and about 10, about 7 and
about 8, or about 8 and about 10. In some embodiments, the ZnSe
shell comprises between 2 and 8 monolayers. In some embodiments,
the ZnSe shell comprises between 4 and 6 monolayers.
[0247] In some embodiments, a ZnSe monolayer has a thickness of
about 0.328 nm.
[0248] In some embodiments, a ZnSe shell has a thickness of between
about 0.08 nm and about 3.5 nm, about 0.08 nm and about 2 nm, about
0.08 nm and about 0.9 nm, about 0.08 nm and about 0.7 nm, about
0.08 nm and about 0.5 nm, about 0.08 nm and about 0.2 nm, about 0.2
nm and about 3.5 nm, about 0.2 nm and about 2 nm, about 0.2 nm and
about 0.9 nm, about 0.2 nm and about 0.7 nm, about 0.2 nm and about
0.5 nm, about 0.5 nm and about 3.5 nm, about 0.5 nm and about 2 nm,
about 0.5 nm and about 0.9 nm, about 0.5 nm and about 0.7 nm, about
0.7 nm and about 3.5 nm, about 0.7 nm and about 2 nm, about 0.7 nm
and about 0.9 nm, about 0.9 nm and about 3.5 nm, about 0.9 nm and
about 2 nm, or about 2 nm and about 3.5 nm.
Production of a ZnS Shell
[0249] In some embodiments, the shell deposited onto the core or
core/shell(s) nanostructure is a ZnS shell.
[0250] In some embodiments, the shell precursors contacted with a
core or core/shell(s) nanostructure to prepare a ZnS shell comprise
a zinc source and a sulfur source.
[0251] In some embodiments, the ZnS shell passivates defects at the
particle surface, which leads to an improvement in the quantum
yield and to higher efficiencies when used in devices such as LEDs
and lasers. Furthermore, spectral impurities which are caused by
defect states may be eliminated by passivation, which increases the
color saturation.
[0252] In some embodiments, the zinc source is a dialkyl zinc
compound. In some embodiments, the zinc source is a zinc
carboxylate. In some embodiments, the zinc source is diethylzinc,
dimethylzinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc
bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc
cyanide, zinc nitrate, zinc oleate, zinc oxide, zinc peroxide, zinc
perchlorate, zinc sulfate, zinc hexanoate, zinc octanoate, zinc
laurate, zinc myristate, zinc palmitate, zinc stearate, zinc
dithiocarbamate, or mixtures thereof. In some embodiments, the zinc
source is zinc oleate, zinc hexanoate, zinc octanoate, zinc
laurate, zinc myristate, zinc palmitate, zinc stearate, zinc
dithiocarbamate, or mixtures thereof. In some embodiments, the zinc
source is zinc oleate.
[0253] In some embodiments, the sulfur source is selected from
elemental sulfur, octanethiol, dodecanethiol, octadecanethiol,
tributylphosphine sulfide, cyclohexyl isothiocyanate,
.alpha.-toluenethiol, ethylene trithiocarbonate, allyl mercaptan,
bis(trimethylsilyl) sulfide, trioctylphosphine sulfide, and
mixtures thereof. In some embodiments, the sulfur source is an
alkyl-substituted zinc dithiocarbamate. In some embodiments, the
sulfur source is octanethiol. In some embodiments, the sulfur
source is tributylphosphine sulfide.
[0254] In some embodiments, the molar ratio of core to zinc source
to prepare a ZnS shell is between about 1:2 and about 1:1000, about
1:2 and about 1:100, about 1:2 and about 1:50, about 1:2 and about
1:25, about 1:2 and about 1:15, about 1:2 and about 1:10, about 1:2
and about 1:5, about 1:5 and about 1:1000, about 1:5 and about
1:100, about 1:5 and about 1:50, about 1:5 and about 1:25, about
1:5 and about 1:15, about 1:5 and about 1:10, about 1:10 and about
1:1000, about 1:10 and about 1:100, about 1:10 and about 1:50,
about 1:10 and about 1:25, about 1:10 and about 1:15, about 1:15
and about 1:1000, about 1:15 and about 1:100, about 1:15 and about
1:50, about 1:15 and about 1:25, about 1:25 and about 1:1000, about
1:25 and about 1:100, about 1:25 and about 1:50, about 1:50 and
about 1:1000, about 1:50 and about 1:100, or about 1:100 and about
1:1000.
[0255] In some embodiments, the molar ratio of core to sulfur
source to prepare a ZnS shell is between about 1:2 and about
1:1000, about 1:2 and about 1:100, about 1:2 and about 1:50, about
1:2 and about 1:25, about 1:2 and about 1:15, about 1:2 and about
1:10, about 1:2 and about 1:5, about 1:5 and about 1:1000, about
1:5 and about 1:100, about 1:5 and about 1:50, about 1:5 and about
1:25, about 1:5 and about 1:15, about 1:5 and about 1:10, about
1:10 and about 1:1000, about 1:10 and about 1:100, about 1:10 and
about 1:50, about 1:10 and about 1:25, about 1:10 and about 1:15,
about 1:15 and about 1:1000, about 1:15 and about 1:100, about 1:15
and about 1:50, about 1:15 and about 1:25, about 1:25 and about
1:1000, about 1:25 and about 1:100, about 1:25 and about 1:50,
about 1:50 and about 1:1000, about 1:50 and about 1:100, or about
1:100 and about 1:1000.
[0256] In some embodiments, the number of monolayers in a ZnS shell
is between about 0.25 and about 10, about 0.25 and about 8, about
0.25 and about 7, about 0.25 and about 6, about 0.25 and about 5,
about 0.25 and about 4, about 0.25 and about 3, about 0.25 and
about 2, about 2 and about 10, about 2 and about 8, about 2 and
about 7, about 2 and about 6, about 2 and about 5, about 2 and
about 4, about 2 and about 3, about 3 and about 10, about 3 and
about 8, about 3 and about 7, about 3 and about 6, about 3 and
about 5, about 3 and about 4, about 4 and about 10, about 4 and
about 8, about 4 and about 7, about 4 and about 6, about 4 and
about 5, about 5 and about 10, about 5 and about 8, about 5 and
about 7, about 5 and about 6, about 6 and about 10, about 6 and
about 8, about 6 and about 7, about 7 and about 10, about 7 and
about 8, or about 8 and about 10. In some embodiments, the ZnS
shell comprises between 2 and 8 monolayers. In some embodiments,
the ZnS shell comprises between 4 and 6 monolayers.
[0257] In some embodiments, a ZnS monolayer has a thickness of
about 0.31 nm.
[0258] In some embodiments, a ZnS shell has a thickness of between
about 0.08 nm and about 3.5 nm, about 0.08 nm and about 2 nm, about
0.08 nm and about 0.9 nm, about 0.08 nm and about 0.7 nm, about
0.08 nm and about 0.5 nm, about 0.08 nm and about 0.2 nm, about 0.2
nm and about 3.5 nm, about 0.2 nm and about 2 nm, about 0.2 nm and
about 0.9 nm, about 0.2 nm and about 0.7 nm, about 0.2 nm and about
0.5 nm, about 0.5 nm and about 3.5 nm, about 0.5 nm and about 2 nm,
about 0.5 nm and about 0.9 nm, about 0.5 nm and about 0.7 nm, about
0.7 nm and about 3.5 nm, about 0.7 nm and about 2 nm, about 0.7 nm
and about 0.9 nm, about 0.9 nm and about 3.5 nm, about 0.9 nm and
about 2 nm, or about 2 nm and about 3.5 nm.
Core/Shell(s) Nanostructures
[0259] In some embodiments, the core/shell(s) nanostructure is a
ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS core/shell nanostructure. In some
embodiments, the core/shell(s) nanostructure is a
ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS core/shell quantum dot.
[0260] In some embodiments, the core/shell(s) nanostructures
display a high photoluminescence quantum yield. In some
embodiments, the core/shell(s) nanostructures display a
photoluminescence quantum yield of between about 30% and about 99%,
about 30% and about 95%, about 30% and about 90%, about 30% and
about 85%, about 30% and about 80%, about 30% and about 60%, about
30% and about 50%, about 30% and about 40%, about 40% and about
99%, about 40% and about 95%, about 40% and about 90%, about 40%
and about 85%, about 40% and about 80%, about 40% and about 60%,
about 40% and about 50%, about 50% and about 99%, about 50% and
about 95%, about 50% and about 90%, about 50% and about 85%, about
60% and about 99%, about 60% and about 95%, about 60% and about
85%, about 80% and about 99%, about 80% and about 90%, about 80%
and about 85%, about 85% and about 99%, or about 85% and about 95%.
In some embodiments, the core/shell(s) nanostructures display a
photoluminescence quantum yield of between about 50% and about 60%.
In some embodiments, the core/shell(s) nanostructures display a
photoluminescence quantum yield of between about 75% and about
90%.
[0261] In some embodiments, the photoluminescence spectrum for the
core/shell(s) nanostructures have a emission maximum between about
300 nm and about 590 nm, about 300 nm and about 550 nm, about 300
nm and about 450 nm, about 450 nm and about 590 nm, about 450 nm
and about 550 nm, or about 550 nm and about 590. In some
embodiments, the photoluminescence spectrum for the core/shell(s)
nanostructures has an emission maximum of between about 420 nm and
about 480 nm. In some embodiments, the photoluminescence spectrum
for the core/shell(s) nanostructures has an emission maximum of
between about 440 nm and about 460 nm. In some embodiments, the
photoluminescence spectrum for the core/shell(s) nanostructures has
an emission maximum of between about 450 nm and about 460 nm.
[0262] The size distribution of the core/shell(s) nanostructures
can be relatively narrow. In some embodiments, the
photoluminescence spectrum of the population or core/shell(s)
nanostructures can have a full width at half-maximum of between
about 10 nm and about 30 nm, about 10 nm and about 25 nm, about 10
nm and about 20 nm, about 10 nm and about 22 nm, about 10 nm and
about 15 nm, about 15 nm and about 30 nm, about 15 nm and about 25
nm, about 15 nm and about 22 nm, about 15 nm and about 20 nm, about
20 nm and about 30 nm, about 20 nm and about 25 nm, about 20 nm and
about 22 nm, about 22 nm and about 30 nm, about 22 nm and about 25
nm, or about 25 nm and about 30 nm. In some embodiments, the
photoluminescence spectrum of the population of core/shell(s)
nanostructures can have a full width at half-maximum of between
about 15 nm and about 22 nm. In some embodiments, the
photoluminescence spectrum of the population of core/shell(s)
nanostructures can have a full width at half-maximum of between
about 20 nm to about 30 nm.
Nanostructure Film
[0263] In some embodiments, the core/shell(s) nanostructures
prepared by the method described herein are incorporated into a
nanostructure film. In some embodiments, the nanostructure film is
incorporated into a quantum dot enhancement film (QDEF).
[0264] In some embodiments, the present disclosure provides a
nanostructure film comprising at least one population of
nanostructures, wherein the nanostructure comprise a core
surrounded by at least one shell, wherein the core comprises
ZnSe.sub.1-xTe.sub.x, wherein 0<x<1, wherein the at least one
shell comprises ZnS or ZnSe, and wherein the full width at half
maximum (FWHM) of the nanostructure is about 20 nm to about 30
nm.
[0265] In some embodiments, the nanostructure is a quantum dot.
[0266] In some embodiments, the present disclosure provides a
nanostructure film comprising:
[0267] (a) at least one population of nanostructures, wherein the
nanostructures comprise a core surrounded by at least one shell,
wherein the core comprises ZnSe.sub.1-xTe.sub.x, wherein
0<x<1, wherein the at least one shell comprises ZnS or ZnSe,
and wherein the full width at half maximum (FWHM) of the
nanostructure is about 20 nm to about 30 nm; and
[0268] (b) at least one organic resin.
[0269] In some embodiments, the nanostructure is a quantum dot.
[0270] In some embodiments, the core/shell(s) nanostructures are
embedded in a matrix. As used herein, the term "embedded" is used
to indicate that the nanostructures are enclosed or encased within
a matrix material that makes up the majority component of the
matrix. In some embodiments, the nanostructures are uniformly
distributed throughout the matrix material. In some embodiments,
the nanostructures are distributed according to an
application-specific uniformity distribution function.
[0271] In some embodiments, the nanostructures can include a
homogenous population having sizes that emit in the blue visible
wavelength spectrum, in the green visible wavelength spectrum, or
in the red visible wavelength spectrum. In some embodiments, the
nanostructures can include a first population of nanostructures
having sizes that emit in the blue visible wavelength spectrum, a
second population of nanostructures having sizes that emit in the
green visible wavelength spectrum, and a third population of
nanostructures having sizes that emit in the red visible wavelength
spectrum.
[0272] The matrix material can be any suitable host matrix material
capable of housing nanostructures. Suitable matrix materials can be
chemically and optically compatible with nanostructures and any
surrounding packaging materials or layers used in applying a
nanostructure film to devices. Suitable matrix materials can
include non-yellowing optical materials that are transparent to
both the primary and secondary light, thereby allowing for both
primary and secondary light to transmit through the matrix
material. Matrix materials can include polymers and organic and
inorganic oxides. Suitable polymers for use in the matrix material
can be any polymer known to the ordinarily skilled artisan that can
be used for such a purpose. The polymer can be substantially
translucent or substantially transparent. Matrix materials can
include, but not limited to, epoxies, acrylates, norbornene,
polyethylene, poly(vinyl butyral):poly(vinyl acetate), polyurea,
polyurethanes; silicones and silicone derivatives including, but
not limited to, amino silicone (AMS), polyphenylmethylsiloxane,
polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane,
silsesquioxanes, fluorinated silicones, and vinyl and hydride
substituted silicones; acrylic polymers and copolymers formed from
monomers including, but not limited to, methylmethacrylate,
butylmethacrylate, and laurylmethacrylate; styrene-based polymers
such as polystyrene, amino polystyrene (APS), and
poly(acrylonitrile ethylene styrene) (AES); polymers that are
cross-linked with bifunctional monomers, such as divinylbenzene;
cross-linkers suitable for cross-linking ligand materials, epoxides
that combine with ligand amines (e.g., APS or polyethylene imine
ligand amines) to form epoxy, and the like.
[0273] In some embodiments, the matrix material includes scattering
microbeads such as TiO.sub.2 microbeads, ZnS microbeads, or glass
microbeads that can improve photo conversion efficiency of the
nanostructure film. In some embodiments, the matrix material can
include light blocking elements.
[0274] In some embodiments, the matrix material can have low oxygen
and moisture permeability, exhibit high photo- and
chemical-stability, exhibit favorable refractive indices, and
adhere to outer surfaces of the nanostructures, thus providing an
air-tight seal to protect the nanostructures. In another
embodiment, the matrix material can be curable with UV or thermal
curing methods to facilitate roll-to-roll processing.
[0275] In some embodiments, a nanostructure film can be formed by
mixing nanostructures in a polymer (e.g., photoresist) and casting
the nanostructure-polymer mixture on a substrate, mixing the
nanostructures with monomers and polymerizing them together, mixing
nanostructures in a sol-gel to form an oxide, or any other method
known to those skilled in the art.
[0276] In some embodiments, the formation of a nanostructure film
can include a film extrusion process. The film extrusion process
can include forming a homogenous mixture of matrix material and
barrier layer coated core-shell nanostructures such as
nanostructures functionalized with a metal halide and/or a metal
carboxylate, introducing the homogenous mixture into a top mounted
hopper that feeds into an extruder. In some embodiments, the
homogenous mixture can be in the form of pellets. The film
extrusion process can further include extruding a nanostructure
film from a slot die and passing an extruded nanostructure film
through chill rolls. In some embodiments, the extruded
nanostructure film can have a thickness less than about 75 .mu.m,
for example, in a range from about 70 .mu.m to about 40 .mu.m,
about 65 .mu.m to about 40 .mu.m, about 60 .mu.m to about 40 .mu.m,
or about 50 .mu.m to about 40 .mu.m. In some embodiments, the
nanostructure film has a thickness less than about 10 .mu.m. In
some embodiments, the formation of the nanostructure film can
optionally include a secondary process followed by the film
extrusion process. The secondary process can include a process such
as co-extrusion, thermoforming, vacuum forming, plasma treatment,
molding, and/or embossing to provide a texture to a top surface of
the nanostructure film layer. The textured top surface
nanostructure film can help to improve, for example defined optical
diffusion property and/or defined angular optical emission property
of the nanostructure film.
Quantum Dot on Glass LCD Display Device
[0277] In some embodiments, the nanostructure film is incorporated
into a quantum dot on glass LCD display device. A LCD display
device can include a nanostructure film formed directly on a light
guide plate (LGP) without necessitating an intermediate substrate
or barrier layer. In some embodiments, a nanostructure film can be
a thin film. In some embodiments, a nanostructure film can have a
thickness of 500 .mu.m or less, 100 .mu.m or less, or 50 .mu.m or
less. In some embodiments, a nanostructure film is a thin film
having a thickness of about 15 .mu.m or less.
[0278] A LGP can include an optical cavity having one or more
sides, including at least a top side, comprising glass. Glass
provides excellent resistance to impurities including moisture and
air. Moreover, glass can be formed as a thin substrate while
maintaining structural rigidity. Therefore, a LGP can be formed at
least partially of a glass surface to provide a substrate having
sufficient barrier and structural properties.
[0279] In some embodiments, a nanostructure film can be formed on a
LGP. In some embodiments, the nanostructure film comprises a
population of nanostructures embedded in a matrix material, such as
a resin. A nanostructure film can be formed on a LGP by any method
known in the art, such as wet coating, painting, spin coating, or
screen printing. After deposition, a resin of a nanostructure film
can be cured. In some embodiments a resin of one or more
nanostructure films can be partially cured, further processed and
then finally cured. The nanostructure films can be deposited as one
layer or as separate layers, and the separate layers can comprise
varying properties. The width and height of the nanostructure films
can be any desired dimensions, depending on the size of the viewing
panel of the display device. For example, the nanostructure films
can have a relatively small surface area in small display device
embodiments such as watches and phones, or the nanostructure films
can have a large surface area for large display device embodiments
such as TVs and computer monitors.
[0280] In some embodiments, an optically transparent substrate is
formed on a nanostructure film by any method known in the art, such
as vacuum deposition, vapor deposition, or the like. An optically
transparent substrate can be configured to provide environmental
sealing to the underlying layers and/or structures of the
nanostructure film. In some embodiments, light blocking elements
can be included in the optically transparent substrate. In some
embodiments, light blocking elements can be included in a second
polarizing filter, which can be positioned between the substrate
and the nanostructure film. In some embodiments, light blocking
elements can be dichroic filters that, for example, can reflect the
primary light (e.g., blue light, UV light, or combination of UV
light and blue light) while transmitting the secondary light. Light
blocking elements can include specific UV light filtering
components to remove any unconverted UV light from the red and
green sub-pixels, and/or the UV light from the blue sub-pixels.
On-Chip and Near Chip Placement of Quantum Dots
[0281] In some embodiments, the nanostructures are incorporated
into display devices by "on-chip" placements. As used herein,
"on-chip" refers to placing nanostructures into an LED cup. In some
embodiments, the nanostructures are dissolved in a resin or a fluid
to fill the LED cup.
[0282] In some embodiments, the nanostructures are incorporated
into display devices by "near-chip" placements. As used herein,
"near-chip" refers to coating the top surface of the LED assembly
with nanostructures such that the outgoing light passes through the
nanostructure film.
Display Device with Nanostructure Color Conversion Layer
[0283] In some embodiments, the present invention provides a
display device comprising:
[0284] (a) a display panel to emit a first light;
[0285] (b) a backlight unit configured to provide the first light
to the display panel; and
[0286] (c) a color filter comprising at least one pixel region
comprising a color conversion layer.
[0287] In some embodiments, the color filter comprises at least 1,
2, 3, 4, 5, 6, 7, 8, 9, or 10 pixel regions. In some embodiments,
when blue light is incident on the color filter, red light, white
light, green light, and/or blue light may be respectively emitted
through the pixel regions. In some embodiments, the color filter is
described in U.S. Patent Appl. Publication No. 2017/153366, which
is incorporated herein by reference in its entirety.
[0288] In some embodiments, each pixel region includes a color
conversion layer. In some embodiments, a color conversion layer
comprises nanostructures described herein configured to convert
incident light into light of a first color. In some embodiments,
the color conversion layer comprises nanostructures described
herein configured to convert incident light into blue light.
[0289] In some embodiments, the display device comprises 1, 2, 3,
4, 5, 6, 7, 8, 9, or 10 color conversion layers. In some
embodiments, the display device comprises 1 color conversion layer
comprising the nanostructures described herein. In some
embodiments, the display device comprises 2 color conversion layers
comprising the nanostructures described herein. In some
embodiments, the display device comprises 3 color conversion layers
comprising the nanostructures described herein. In some
embodiments, the display device comprises 4 color conversion layers
comprising the nanostructures described herein. In some
embodiments, the display device comprises at least one red color
conversion layer, at least one green color conversion layer, and at
least one blue color conversion layer.
[0290] In some embodiments, the color conversion layer has a
thickness between about 3 .mu.m and about 10 about 3 .mu.m and
about 8 about 3 .mu.m and about 6 about 6 .mu.m and about 10 about
6 .mu.m and about 8 or about 8 .mu.m and about 10 In some
embodiments, the color conversion layer has a thickness between
about 3 .mu.m and about 10 .mu.m.
[0291] The nanostructure color conversion layer can be deposited by
any suitable method known in the art, including but not limited to
painting, spray coating, solvent spraying, wet coating, adhesive
coating, spin coating, tape-coating, roll coating, flow coating,
inkjet printing, photoresist patterning, drop casting, blade
coating, mist deposition, or a combination thereof. In some
embodiments, the nanostructure color conversion layer is deposited
by photoresist patterning. In some embodiments, nanostructure color
conversion layer is deposited by inkjet printing.
Inkjet Printing
[0292] The formation of thin films using dispersions of
nanostructures in organic solvents is often achieved by coating
techniques such as spin coating. However, these coating techniques
are generally not suitable for the formation of thin films over a
large area and do not provide a means to pattern the deposited
layer and thus, are of limited use. Inkjet printing allows for
precisely patterned placement of thin films on a large scale at low
cost. Inkjet printing also allows for precise patterning of
nanostructure layers, allows printing pixels of a display, and
eliminates photopatterning. Thus, inkjet printing is very
attractive for industrial application--particularly in display
applications.
[0293] Solvents commonly used for inkjet printing are dipropylene
glycol monomethyl ether acetate (DPMA), polyglycidyl methacrylate
(PGMA), diethylene glycol monoethyl ether acetate (EDGAC), and
propylene glycol methyl ether acetate (PGMEA). Volatile solvents
are also frequently used in inkjet printing because they allow
rapid drying. Volatile solvents include ethanol, methanol,
1-propanol, 2-propanol, acetone, methyl ethyl ketone, methyl
isobutyl ketone, ethyl acetate, and tetrahydrofuran. Conventional
nanostructures generally cannot be dissolved in these solvents.
However, the increased hydrophilicity of the nanostructures
described herein allows for increased solubility in these
solvents.
[0294] In some embodiments, the nanostructures described herein
used for inkjet printing are dispersed in a solvent selected from
DPMA, PGMA, EDGAC, PGMEA, ethanol, methanol, 1-propanol,
2-propanol, acetone, methyl ethyl ketone, methyl isobutyl ketone,
ethyl acetate, tetrahydrofuran, chloroform, chlorobenzene,
cyclohexane, hexane, heptane, octane, hexadecane, undecane, decane,
dodecane, xylene, toluene, benzene, octadecane, tetradecane, butyl
ether, or combinations thereof. In some embodiments, the
nanostructures comprising a poly(alkylene oxide) ligands described
herein used for inkjet printing are dispersed in a solvent selected
from DPMA, PGMA, EDGAC, PGMEA, ethanol, methanol, 1-propanol,
2-propanol, acetone, methyl ethyl ketone, methyl isobutyl ketone,
ethyl acetate, tetrahydrofuran, or combinations thereof.
[0295] In order to be applied by inkjet printing or
microdispensing, the inkjet compositions comprising nanostructures
should be dissolved in a suitable solvent. The solvent must be able
to disperse the nanostructure composition and must not have any
detrimental effect on the chosen print head.
[0296] In some embodiments, the inkjet composition further
comprises one or more additional components such as surface-active
compounds, lubricating agents, wetting agents, dispersing agents,
hydrophobing agents, adhesive agents, flow improvers, defoaming
agents, deaerators, diluents, auxiliaries, colorants, dyes,
pigments, sensitizers, stabilizers, and inhibitors.
[0297] In some embodiments, the nanostructure compositions
described herein comprise by weight of the inkjet composition
between about 0.01% and about 20%. In some embodiments, the
nanostructures described herein comprise by weight of the inkjet
composition between about 0.01% and about 20%, about 0.01% and
about 15%, about 0.01% and about 10%, about 0.01% and about 5%,
about 0.01% and about 2%, about 0.01% and about 1%, about 0.01% and
about 0.1%, about 0.01% and about 0.05%, about 0.05% and about 20%,
about 0.05% and about 15%, about 0.05% and about 10%, about 0.05%
and about 5%, about 0.05% and about 2%, about 0.05% and about 1%,
about 0.05% and about 0.1%, about 0.1% and about 20%, about 0.1%
and about 15%, about 0.1% and about 10%, about 0.1% and about 5%,
about 0.1% and about 2%, about 0.1% and about 1%, about 0.5% and
about 20%, about 0.5% and about 15%, about 0.5% and about 10%,
about 0.5% and about 5%, about 0.5% and about 2%, about 0.5% and
about 1%, about 1% and about 20%, about 1% and about 15%, about 1%
and about 10%, about 1% and about 5%, about 1% and about 2%, about
2% and about 20%, about 2% and about 15%, about 2% and about 10%,
about 2% and about 5%, about 5% and about 20%, about 5% and about
15%, about 5% and about 10%, about 10% and about 20%, about 10% and
about 15%, or about 15% and 20%.
[0298] In some embodiments, the inkjet composition comprising a
nanostructure or a nanostructure composition described herein is
used in the formulation of an electronic device. In some
embodiments, the inkjet composition comprising a nanostructure or a
nanostructure composition described herein is used in the
formulation of an electronic device selected from the group
consisting of a nanostructure film, a display device, a lighting
device, a backlight unit, a color filter, a surface light-emitting
device, an electrode, a magnetic memory device, and a battery. In
some embodiments, the inkjet composition comprising a nanostructure
composition described herein is used in the formulation of a
light-emitting device.
Nanostructure Molded Article
[0299] In some embodiments, the nanostructure composition is used
to form a nanostructure molded article. In some embodiments, the
nanostructure molded article is a liquid crystal display (LCD) or a
light emitting diode (LED). In some embodiments, the nanostructure
composition is used to form the emitting layer of an illumination
device. The illumination device can be used in a wide variety of
applications, such as flexible electronics, touchscreens, monitors,
televisions, cellphones, and any other high definition displays. In
some embodiments, the illumination device is a light emitting diode
or a liquid crystal display. In some embodiments, the illumination
device is a quantum dot light emitting diode (QLED). An example of
a QLED is disclosed in U.S. patent application Ser. No. 15/824,701,
which is incorporated herein by reference in its entirety.
[0300] In some embodiments, the present disclosure provides a light
emitting diode comprising:
[0301] (a) a first conductive layer;
[0302] (b) a second conductive layer; and
[0303] (c) an emitting layer between the first conductive layer and
the second conductive layer, wherein the emitting layer comprises
at least one population of nanostructures, wherein the
nanostructures comprise a core surrounded by at least one shell,
wherein the core comprises ZnSe.sub.1-xTe.sub.x, wherein
0<x<1, wherein the at least one shell comprises ZnS or ZnSe,
and wherein the full width at half maximum (FWHM) of the
nanostructure is about 20 nm to about 30 nm.
[0304] In some embodiments, the emitting layer is a nanostructure
film.
[0305] In some embodiments, the light emitting diode comprises a
first conductive layer, a second conductive layer, and an emitting
layer, wherein the emitting layer is arranged between the first
conductive layer and the second conductive layer. In some
embodiments, the emitting layer is a thin film.
[0306] In some embodiments, the light emitting diode comprises
additional layers between the first conductive layer and the second
conductive layer such as a hole injection layer, a hole transport
layer, and an electron transport layer. In some embodiments, the
hole injection layer, the hole transport layer, and the electron
transport layer are thin films. In some embodiments, the layers are
stacked on a substrate.
[0307] When voltage is applied to the first conductive layer and
the second conductive layer, holes injected at the first conductive
layer move to the emitting layer via the hole injection layer
and/or the hole transport layer, and electrons injected from the
second conductive layer move to the emitting layer via the electron
transport layer. The holes and electrons recombine in the emitting
layer to generate excitons.
Making a Nanostructure Layer
[0308] In some embodiments, the nanostructure layer can be embedded
in a polymeric matrix. As used herein, the term "embedded" is used
to indicate that the nanostructure population is enclosed or
encased with the polymer that makes up the majority of the
components of the matrix. In some embodiments, at least one
nanostructure population is suitably uniformly distributed
throughout the matrix. In some embodiments, the at least one
nanostructure population is distributed according to an
application-specific distribution. In some embodiments, the
nanostructures are mixed in a polymer and applied to the surface of
a substrate.
[0309] In some embodiments, a nanostructure composition is
deposited to form a nanostructure layer. In some embodiments, a
nanostructure composition can be deposited by any suitable method
known in the art, including but not limited to painting, spray
coating, solvent spraying, wet coating, adhesive coating, spin
coating, tape-coating, roll coating, flow coating, inkjet vapor
jetting, drop casting, blade coating, mist deposition, or a
combination thereof. The nanostructure composition can be coated
directly onto the desired layer of a substrate. Alternatively, the
nanostructure composition can be formed into a solid layer as an
independent element and subsequently applied to the substrate. In
some embodiments, the nanostructure composition can be deposited on
one or more barrier layers.
[0310] In some embodiments, the nanostructure layer is cured after
deposition. Suitable curing methods include photo-curing, such as
UV curing, and thermal curing. Traditional laminate film processing
methods, tape-coating methods, and/or roll-to-roll fabrication
methods can be employed in forming a nanostructure layer.
Spin Coating
[0311] In some embodiments, the nanostructure composition is
deposited onto a substrate using spin coating. In spin coating a
small amount of material is typically deposited onto the center of
a substrate loaded onto a machine called the spinner which is
secured by a vacuum. A high speed of rotation is applied on the
substrate through the spinner which causes centripetal force to
spread the material from the center to the edge of the substrate.
While most of the material is spun off, a certain amount remains of
the substrate, forming a thin film of material on the surface as
the rotation continues. The final thickness of the film is
determined by the nature of the deposited material and the
substrate in addition to the parameters chosen for the spin process
such as spin speed, acceleration, and spin time. In some
embodiments, a spin speed of 1500 to 6000 rpm is used with a spin
time of 10-60 seconds.
Mist Deposition
[0312] In some embodiments, the nanostructure composition is
deposited onto a substrate using mist deposition. Mist deposition
takes place at room temperature and atmospheric pressure and allows
precise control over film thickness by changing the process
conditions. During mist deposition, a liquid source material is
turned into a very fine mist and carried to the deposition chamber
by nitrogen gas. The mist is then drawn to a wafer surface by a
high voltage potential between the field screen and the wafer
holder. Once the droplets coalesce on the wafer surface, the wafer
is removed from the chamber and thermally cured to allow the
solvent to evaporate. The liquid precursor is a mixture of solvent
and material to be deposited. It is carried to the atomizer by
pressurized nitrogen gas. Price, S. C., et al., "Formation of
Ultra-Thin Quantum Dot Films by Mist Deposition," ESC Transactions
11:89-94 (2007).
Spray Coating
[0313] In some embodiments, the nanostructure composition is
deposited onto a substrate using spray coating. The typical
equipment for spray coating comprises a spray nozzle, an atomizer,
a precursor solution, and a carrier gas. In the spray deposition
process, a precursor solution is pulverized into micro sized drops
by means of a carrier gas or by atomization (e.g., ultrasonic, air
blast, or electrostatic). The droplets that come out of the
atomizer are accelerated by the substrate surface through the
nozzle by help of the carrier gas which is controlled and regulated
as desired. Relative motion between the spray nozzle and the
substrate is defined by design for the purpose of full coverage on
the substrate.
[0314] In some embodiments, application of the nanostructure
composition further comprises a solvent. In some embodiments, the
solvent for application of the nanostructure composition is water,
organic solvents, inorganic solvents, halogenated organic solvents,
or mixtures thereof. Illustrative solvents include, but are not
limited to, water, D.sub.2O, acetone, ethanol, dioxane, ethyl
acetate, methyl ethyl ketone, isopropanol, anisole,
.gamma.-butyrolactone, dimethylformamide, N-methylpyrrolidinone,
dimethylacetamide, hexamethylphosphoramide, toluene,
dimethylsulfoxide, cyclopentanone, tetramethylene sulfoxide,
xylene, .epsilon.-caprolactone, tetrahydrofuran,
tetrachloroethylene, chloroform, chlorobenzene, dichloromethane,
1,2-dichloroethane, 1,1,2,2-tetrachloroethane, or mixtures
thereof.
[0315] In some embodiments, the nanostructure compositions are
thermally cured to form the nanostructure layer. In some
embodiments, the compositions are cured using UV light. In some
embodiments, the nanostructure composition is coated directly onto
a barrier layer of a nanostructure film, and an additional barrier
layer is subsequently deposited upon the nanostructure layer to
create the nanostructure film. A support substrate can be employed
beneath the barrier film for added strength, stability, and coating
uniformity, and to prevent material inconsistency, air bubble
formation, and wrinkling or folding of the barrier layer material
or other materials. Additionally, one or more barrier layers are
preferably deposited over a nanostructure layer to seal the
material between the top and bottom barrier layers. Suitably, the
barrier layers can be deposited as a laminate film and optionally
sealed or further processed, followed by incorporation of the
nanostructure film into the particular lighting device. The
nanostructure composition deposition process can include additional
or varied components, as will be understood by persons of ordinary
skill in the art. Such embodiments will allow for in-line process
adjustments of the nanostructure emission characteristics, such as
brightness and color (e.g., to adjust the quantum dot film white
point), as well as the nanostructure film thickness and other
characteristics. Additionally, these embodiments will allow for
periodic testing of the nanostructure film characteristics during
production, as well as any necessary toggling to achieve precise
nanostructure film characteristics. Such testing and adjustments
can also be accomplished without changing the mechanical
configuration of the processing line, as a computer program can be
employed to electronically change the respective amounts of
mixtures to be used in forming a nanostructure film.
Barrier Layers
[0316] In some embodiments, the molded article comprises one or
more barrier layers disposed on either one or both sides of the
nanostructure layer. Suitable barrier layers protect the
nanostructure layer and the molded article from environmental
conditions such as high temperatures, oxygen, and moisture.
Suitable barrier materials include non-yellowing, transparent
optical materials which are hydrophobic, chemically and
mechanically compatible with the molded article, exhibit photo- and
chemical-stability, and can withstand high temperatures. In some
embodiments, the one or more barrier layers are index-matched to
the molded article. In some embodiments, the matrix material of the
molded article and the one or more adjacent barrier layers are
index-matched to have similar refractive indices, such that most of
the light transmitting through the barrier layer toward the molded
article is transmitted from the barrier layer into the
nanostructure layer. This index-matching reduces optical losses at
the interface between the barrier and matrix materials.
[0317] The barrier layers are suitably solid materials, and can be
a cured liquid, gel, or polymer. The barrier layers can comprise
flexible or non-flexible materials, depending on the particular
application. Barrier layers are preferably planar layers, and can
include any suitable shape and surface area configuration,
depending on the particular lighting application. In some
embodiments, the one or more barrier layers will be compatible with
laminate film processing techniques, whereby the nanostructure
layer is disposed on at least a first barrier layer, and at least a
second barrier layer is disposed on the nanostructure layer on a
side opposite the nanostructure layer to form the molded article
according to one embodiment. Suitable barrier materials include any
suitable barrier materials known in the art. In some embodiments,
suitable barrier materials include glasses, polymers, and oxides.
Suitable barrier layer materials include, but are not limited to,
polymers such as polyethylene terephthalate (PET); oxides such as
silicon oxide, titanium oxide, or aluminum oxide (e.g., SiO.sub.2,
Si.sub.2O.sub.3, TiO.sub.2, or Al.sub.2O.sub.3); and suitable
combinations thereof. Preferably, each barrier layer of the molded
article comprises at least 2 layers comprising different materials
or compositions, such that the multi-layered barrier eliminates or
reduces pinhole defect alignment in the barrier layer, providing an
effective barrier to oxygen and moisture penetration into the
nanostructure layer. The nanostructure layer can include any
suitable material or combination of materials and any suitable
number of barrier layers on either or both sides of the
nanostructure layer. The materials, thickness, and number of
barrier layers will depend on the particular application, and will
suitably be chosen to maximize barrier protection and brightness of
the nanostructure layer while minimizing thickness of the molded
article. In preferred embodiments, each barrier layer comprises a
laminate film, preferably a dual laminate film, wherein the
thickness of each barrier layer is sufficiently thick to eliminate
wrinkling in roll-to-roll or laminate manufacturing processes. The
number or thickness of the barriers may further depend on legal
toxicity guidelines in embodiments where the nanostructures
comprise heavy metals or other toxic materials, which guidelines
may require more or thicker barrier layers. Additional
considerations for the barriers include cost, availability, and
mechanical strength.
[0318] In some embodiments, the nanostructure film comprises two or
more barrier layers adjacent each side of the nanostructure layer,
for example, two or three layers on each side or two barrier layers
on each side of the nanostructure layer. In some embodiments, each
barrier layer comprises a thin glass sheet, e.g., glass sheets
having a thickness of about 100 .mu.m, 100 .mu.m or less, or 50
.mu.m or less.
[0319] Each barrier layer of the molded article can have any
suitable thickness, which will depend on the particular
requirements and characteristics of the lighting device and
application, as well as the individual film components such as the
barrier layers and the nanostructure layer, as will be understood
by persons of ordinary skill in the art. In some embodiments, each
barrier layer can have a thickness of 50 .mu.m or less, 40 .mu.m or
less, 30 .mu.m or less, 25 .mu.m or less, 20 .mu.m or less, or 15
.mu.m or less. In certain embodiments, the barrier layer comprises
an oxide coating, which can comprise materials such as silicon
oxide, titanium oxide, and aluminum oxide (e.g., Sift,
Si.sub.2O.sub.3, TiO.sub.2, or Al.sub.2O.sub.3). The oxide coating
can have a thickness of about 10 .mu.m or less, 5 .mu.m or less, 1
.mu.m or less, or 100 nm or less. In certain embodiments, the
barrier comprises a thin oxide coating with a thickness of about
100 nm or less, 10 nm or less, 5 nm or less, or 3 nm or less. The
top and/or bottom barrier can consist of the thin oxide coating, or
may comprise the thin oxide coating and one or more additional
material layers.
Molded Articles with Improved Properties
[0320] In some embodiments, a molded article prepared using the
nanostructures shows an EQE of between about 1.5% and about 20%,
about 1.5% and about 15%, about 1.5% and about 12%, about 1.5% and
about 10%, about 1.5% and about 8%, about 1.5% and about 4%, about
1.5% and about 3%, about 3% and about 20%, about 3% and about 15%,
about 3% and about 12%, about 3% and about 10%, about 3% and about
8%, about 8% and about 20%, about 8% and about 15%, about 8% and
about 12%, about 8% and about 10%, about 10% and about 20%, about
10% and about 15%, about 10% and about 12%, about 12% and about
20%, about 12% and about 15%, or about 15% and about 20%. In some
embodiments, the nanostructure is a quantum dot. In some
embodiments, the molded article is a light emitting diode.
[0321] In some embodiments, a molded article prepared using the
nanostructures shows a photoluminescence spectrum with an emission
maximum of between 450 nm and 550 nm. In some embodiments, a molded
article prepared using the nanostructures shows a photoluminescence
spectrum with an emission maximum of between 450 nm and 460 nm. In
some embodiments, the photoluminescence spectrum for the
core/shell(s) nanostructures has an emission maximum of between
about 450 nm and about 460 nm.
[0322] The following examples are illustrative and non-limiting, of
the products and methods described herein. Suitable modifications
and adaptations of the variety of conditions, formulations, and
other parameters normally encountered in the field and which are
obvious to those skilled in the art in view of this disclosure are
within the spirit and scope of the invention.
EXAMPLES
Example 1
Synthesis of ZnSe.sub.1-xTe.sub.x Alloy Nanostructures Using
Co-injection Method
[0323] The TOPTe precursor mixture was prepared by first diluting
TOPTe (1.0 M Te, 460 .mu.L) with 5.0 mL dried and distilled
oleylamine. Lithium triethylborohydride (1.0 M in THF, 460 .mu.L)
was added to this solution which resulted in a deeply purple
solution. Finally, zinc oleate (0.5 M in TOP, 920 .mu.L) was added
which resulted in a colorless opaque viscous gel which can be drawn
into a syringe.
[0324] Oleylamine (30.0 mL) was added to a 250 mL three-neck flask
and degassed under vacuum at 110.degree. C. for 30 minutes. The
mixture was heated to 300.degree. C. under nitrogen flow. Once this
temperature was reached, a solution of trioctylphosphine selenide
(TOPSe, 5.4 mmol) and diphenylphosphine (535 .mu.L) in TOP (5.8 mL
total) was added to the flask. Once the temperature rebounded to
300.degree. C., the TOPTe precursor formulation described above and
a solution of diethylzinc (590 .mu.L) in TOP (2.0 mL) were quickly
and simultaneously injected from separate syringes. The temperature
was set to 280.degree. C. and after 5 minutes an infusion of a
solution of diethylzinc (588 .mu.L) and TOPSe (8.45 mmol) in TOP
(7.6 mL total) was started at a rate of 1.0 mL/minute with a 10
minute break after addition of 7.6 mL. After the precursor infusion
was finished the reaction mixture was held at 280.degree. C. for 5
minutes and then cooled to room temperature. The growth solution
was diluted with an equal volume of toluene, and the nanocrystals
were precipitated by addition of ethanol. After centrifugation the
supernatant was discarded, and the nanocrystals were re-dispersed
in toluene. The concentration was measured as the dry weight by
evaporating the solvent off an aliquot. The dried material was
further subjected to thermogravimetric analysis to determine the
inorganic content.
Example 2
Synthesis of ZnSe.sub.1-xTe.sub.x Alloy Nanostructures Using Offset
Injection Method
[0325] The TOPTe precursor mixture was prepared by first diluting
TOPTe (1.0 M Te, 460 .mu.L) with 5.0 mL dried and distilled
oleylamine. Lithium triethylborohydride (1.0 M in THF, 460 .mu.L)
was added to this solution which resulted in a deeply purple
solution. Finally, zinc oleate (0.5 M in TOP, 920 .mu.L) was added
which resulted in a colorless opaque viscous gel which can be drawn
into a syringe.
[0326] Oleylamine (30 mL) was added to a 100 mL three-neck flask
and degassed under vacuum at 110.degree. C. for 30 minutes. The
mixture was heated to 300.degree. C. under nitrogen flow. Once this
temperature was reached, a solution of trioctylphosphine selenide
(TOPSe, 5.4 mmol) and diphenylphosphine (535 .mu.L) in TOP (5.8 mL
total) was added to the flask. Once the temperature rebounded to
300.degree. C., the TOPTe precursor formulation described above was
quickly injected. After 3 seconds, a solution of diethylzinc (590
.mu.L) in TOP (2.0 mL) was injected. The temperature was set to
280.degree. C. and after 5 minutes an infusion of a solution of
diethylzinc (588 .mu.L) and TOPSe (8.45 mmol) in TOP (7.6 mL total)
was started at a rate of 1.0 mL/minute with a 10 minute break after
addition of 7.6 mL. After the precursor infusion was finished the
reaction mixture was held at 280.degree. C. for 5 minutes and then
cooled to room temperature. The growth solution was diluted with an
equal volume of toluene, and the nanocrystals were precipitated by
addition of ethanol. After centrifugation the supernatant was
discarded, and the nanocrystals were re-dispersed in toluene. The
concentration was measured as the dry weight by evaporating the
solvent off an aliquot. The dried material was further subjected to
thermogravimetric analysis to determine the inorganic content.
Example 3
Synthesis of ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS Core/Shell
Nanostructures
[0327] Coating a ZnSe shell or a ZnSe/ZnS multi-shell on
ZnSe.sub.1-xTe.sub.x alloy nanocrystals was performed using the
procedure described in U.S. Patent Application Publication No.
2017/066965.
Example 4
Properties of ZnSe.sub.1-xTe.sub.x Core/Shell(s) Nanostructures
[0328] The solution photoluminescence spectra of the
ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS core/shell/shell nanostructures
prepared using the co-injection method and the offset inject method
are shown in FIG. 2. As shown in FIG. 2, a red shift is achieved
with the co-injection and the offset injection method. The offset
injection method resulted in a narrower peak, because the formation
of ZnTe was facilitated. The optical properties of the
ZnSe.sub.1-xTe.sub.x/ZnSe core/shell or
ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS core/shell/shell nanostructures can
be tuned by varying the number of shell monolayers as shown in
TABLE 1.
TABLE-US-00001 TABLE 1 ZnSe ZnS Te Mono- Mono- PWL FWHM Example
(mol %) layers layers (nm) MF.sub.x (nm) QY 1 8 4 0 449 None 21 66%
2 8 6 0 450 None 18 60% 3 8 6 0 451 ZrF.sub.4 19 71% 4 8 6 0 451
ZnF.sub.2 16 64% 5 8 4 4 445 None 19 48% 6 8 6 6 446 None 19 47% 7
8 6 6 447 ZrF.sub.4 21 53% 8 8 6 6 447 HfF.sub.4 21 52% 9 8 6 6 443
ZnF.sub.2 20 40% 10 8 6 6 445 ZrF.sub.4 19 54%
Example 5
ZnSe.sub.1-xTe.sub.x Alloy Nanocrystals and
ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS Quantum Dots with Low FWHM and High
QY
[0329] A: Synthesis of ZnSe.sub.1-xTe.sub.x Alloy Nanocrystals
Using Reduced TOP-Te
[0330] The Te precursor mixture was prepared by first diluting
TOPTe (1 M Te, 690 .mu.L) with 4.0 mL dried and distilled
oleylamine. Lithium triethylborohydride (1 M in THF, 690 .mu.L) was
added to this solution which resulted in a deeply purple solution.
Finally, zinc oleate (0.5 M in TOP, 1180 .mu.L) was added which
resulted in a colorless opaque viscous gel which could be drawn
into a syringe. (In entry 7 of Table 2 below, 1036 .mu.l TOPTe,
1036 .mu.l LiEt.sub.3BH and 2.08 ml ZnOA.sub.2/TOP were used
instead.)
[0331] Oleylamine (30 mL) and anhydrous zinc fluoride (118 mg, 1.04
mmol) were added to a 250 mL three neck flask and degassed under
vacuum at 110.degree. C. for 30 min. (Entry 7 contained no
ZnF.sub.2; all others did.) Then the mixture was heated to
300.degree. C. under nitrogen flow. Once this temperature was
reached, a solution of trioctylphosphine selenide (TOPSe, 5.4 mmol)
and diphenylphosphine (535 uL) in TOP (5.8 mL total) were added to
the flask. Once the temperature rebounded to 280.degree. C., the Te
precursor formulation described above was quickly injected. After 3
seconds, a solution of diethyl zinc (590 .mu.L) in TOP (2.0 mL) was
quickly injected. The temperature was set to 280.degree. C. and
after 5 min the infusion of a solution of diethylzinc (588 .mu.L)
and TOPSe (8.4 mmol) in TOP (7.6 mL total) was started at a rate of
1.0 mL/min until complete addition of the full 7.6 mL. After the
precursor infusion was finished, the reaction mixture was held at
280.degree. C. for 5 min and then cooled to room temperature. The
growth solution was diluted with an equal volume of toluene (60
mL), and the nanocrystals were precipitated by addition of ethanol
(120 mL). After centrifugation the supernatant was discarded, and
the nanocrystals were redispersed in hexane (5 mL). The
concentration was measured as the dry weight by evaporating the
solvent off an aliquot. The dried material was further subjected to
thermogravimetric analysis to determine the inorganic content.
B: Synthesis of ZnSe.sub.1-xTe.sub.x/ZnSe Buffered Nanocrystals
[0332] This example describes a coating of a single monolayer ZnSe
buffer layer on ZnSe.sub.1-xTe.sub.x alloy nanocrystals of 2.3 nm
average diameter with a target shell thickness of 1 ML ZnSe.
(Entries 1 and 3-7 of Table 2 include this sequence of
reactions.)
[0333] A 100 mL three neck flask was charged with zinc oleate (6.23
g), lauric acid (3.96 g), trioctylphosphine oxide (4.66 g),
zirconium fluoride (644 mg) and TOP (9.4 mL). (The reactions for
entries 1 and 6 of Table 2 did not contain lauric acid.) The flask
was then subjected to three vacuum and nitrogen backfill cycles
before heating to 100.degree. C. and then degassed for 30 min. The
reaction mixture was placed under a blanket of nitrogen and a
solution of ZnSe.sub.1-xTe.sub.x cores (4.0 mL, 28.0 mg/mL in
hexane) was mixed with TOP-Se (1.8 ml of 0.3M selenium in TOP) and
added to the flask. The flask was then evacuated for 2 min and then
heated to 310.degree. C. under nitrogen flow. Once this temperature
was reached, the solution was immediately cooled to room
temperature. The reaction mixture was diluted with toluene (45 mL).
The largest core/shell nanocrystals were precipitated by addition
of ethanol (64 mL) and then isolated by centrifugation, decantation
of the supernatant, and disposal of the pelletized nanocrystals.
The supernatant from the previous step was then fully precipitated
by the addition of ethanol (75 ml) and then isolated by
centrifugation, decantation of the supernatant, and redispersion in
hexane (5 ml). This solution was filtered through a PTFE 0.45 .mu.m
syringe filter. The concentration was measured as the dry weight by
evaporating the solvent off an aliquot. The dried material was
further subjected to thermogravimetric analysis to determine the
inorganic content.
C: Synthesis of ZnSe.sub.1-xTe.sub.x/ZnSe Buffered Nanocrystals
[0334] This example describes a coating of a ZnSe buffer layer on
ZnSe.sub.1-xTe.sub.x alloy nanocrystals of 4.0 nm average diameter
with a target shell thickness of 4 ML ZnSe.
[0335] A 100 mL three neck flask was charged with zinc oleate (6.23
g), trioctylphosphine oxide (4.66 g), zirconium fluoride (644 mg),
and TOP (9.4 mL). (In some cases, zinc fluoride (333.8 mg) was also
added; the reaction leading to Table 2 entry #2 also contained
lauric acid (3.39 g), while the remaining reactions did not; the
reactions leading to Table 2 entry 4 contained tri-n-octylamine
(TOA) in place of trioctylphosphine oxide; and the reactions
leading to Table 2 entries 3-5 contained both zirconium fluoride
and zinc fluoride.) The flask was then subjected to three vacuum
and nitrogen backfill cycles before heating to 100.degree. C. and
degassing for 30 min. The reaction mixture was placed under a
blanket of nitrogen and a solution of ZnSe.sub.1-xTe.sub.x cores
(4.0 mL, 28.0 mg/mL in hexane) mixed with TOP-Se (1.8 ml of 0.3M
selenium in TOP) was added to the flask. The flask was evacuated
for 2 min and then heated to 310.degree. C. under nitrogen flow.
Once this temperature was reached, the slow infusion of TOP-Se
(10.4 mL, 0.3 M in TOP) with a rate of 0.325 mL/min was started.
After the selenium infusion was finished, the reaction was held at
310.degree. C. for 5 min and then cooled to room temperature. (The
reaction mixtures leading to Table 2 entries 3-5 were held at
340.degree. C.) The reaction mixture was diluted with toluene (45
mL). The core/shell nanocrystals were precipitated by addition of
ethanol (135 mL) and then isolated by centrifugation, decantation
of the supernatant, and redispersion of the nanocrystals in hexane
(5 mL). This solution was filtered through a PTFE 0.22 .mu.m
syringe filter and the concentration is measured as the dry weight
by evaporating the solvent off an aliquot. The dried material was
further subjected to thermogravimetric analysis to determine the
inorganic content.
D: Synthesis of ZnSe.sub.1-xTe.sub.x/ZnSe/ZnS core/shell
nanocrystals
[0336] This example describes the coating of a ZnS shell on
ZnSe.sub.1-xTe.sub.x/ZnSe alloy nanocrystals of 6.1 nm average
diameter with a target shell thickness of 2-4 ML ZnS. (Table 2
entries 1-3, and 5.)
[0337] A 25 mL three neck flask was charged with zinc oleate (375
mg), trioctylphosphine oxide (281 mg), lauric acid (259 mg), zinc
fluoride (648 mg), and TOP (0.566 mL). (Only the reaction mixture
leading to Table 2 entry #2 contained lauric acid in this step; the
reaction mixtures leading to Table 2 entries 3 and 5 contained 389
mg zinc fluoride.) In the reaction mixtures leading to Table 2
entries 3 and 5, zirconium fluoride (75 mg) was also added. The
flask was then subjected to three vacuum and nitrogen backfill
cycles before heating to 100.degree. C. and degassing for 30 min.
The reaction mixture was placed under a blanket of nitrogen and a
solution of ZnSe.sub.1-xTe.sub.x cores (obtained from C, above,
0.30 mL, 216.0 mg/mL in hexane) mixed with zinc oleate/TOP-S (0.064
ml of 2.0M sulfur in TOP+0.254 ml 0.5M zinc oleate in TOP) was
added to the flask. The flask was evacuated for 2 min and then
heated to 310.degree. C. under nitrogen flow. Once this temperature
was reached, the slow infusion of zinc oleate/TOP-S (2 mL, 0.3 M in
TOP) with a rate of 0.103 mL/min was started. After the sulfur
infusion was finished, the reaction was held at 310.degree. C. for
5 min and then cooled to room temperature. (The reaction mixtures
leading to Table 2 entries 3 & 5 were held at 340.degree. C.)
The reaction mixture was diluted with toluene (5 mL). The
core/shell nanocrystals were precipitated by addition of ethanol
(10 mL) and then isolated by centrifugation, decantation of the
supernatant, and redispersion of the nanocrystals in hexane (5 mL).
The precipitation was repeated once with ethanol (10 mL), and the
nanocrystals were finally redispersed in octane (3 mL). This
solution was filtered through a PTFE 0.22 .mu.m syringe filter and
the concentration was adjusted to 18 mg/mL after measuring the dry
weight of an aliquot.
[0338] The optical properties of the nanostructures made according
to this example are shown in Table 2. Unexpectedly, these
nanostructures exhibited much higher QY compared to the
nanostructures made according to Example 4.
TABLE-US-00002 TABLE 2 # PWL/nm FWHM/nm QY/% 1 445 25 81 2 448 28
88 3 451 28 87 4 452 30 89 5 454 25 83 6 456 30 78 7 461 30 74
[0339] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. It will be apparent to persons
skilled in the relevant art that various changes in form and detail
can be made therein without departing from the spirit and scope of
the invention. Thus, the breadth and scope should not be limited by
any of the above-described exemplary embodiments, but should be
defined only in accordance with the following claims and their
equivalents.
[0340] All publications, patents and patent applications mentioned
in this specification are indicative of the level of skill of those
skilled in the art to which this invention pertains, and are herein
incorporated by reference to the same extent as if each individual
publication, patent or patent application was specifically and
individually indicated to be incorporated by reference.
* * * * *